http://git-wip-us.apache.org/repos/asf/zookeeper/blob/4607a3e1/src/docs/src/documentation/content/xdocs/zookeeperQuotas.xml ---------------------------------------------------------------------- diff --git a/src/docs/src/documentation/content/xdocs/zookeeperQuotas.xml b/src/docs/src/documentation/content/xdocs/zookeeperQuotas.xml deleted file mode 100644 index 7668e6a..0000000 --- a/src/docs/src/documentation/content/xdocs/zookeeperQuotas.xml +++ /dev/null @@ -1,71 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> - <!-- - Copyright 2002-2004 The Apache Software Foundation Licensed under the - Apache License, Version 2.0 (the "License"); you may not use this file - except in compliance with the License. You may obtain a copy of the - License at http://www.apache.org/licenses/LICENSE-2.0 Unless required - by applicable law or agreed to in writing, software distributed under - the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR - CONDITIONS OF ANY KIND, either express or implied. See the License for - the specific language governing permissions and limitations under the - License. - --> - <!DOCTYPE article PUBLIC "-//OASIS//DTD Simplified DocBook XML V1.0//EN" - "http://www.oasis-open.org/docbook/xml/simple/1.0/sdocbook.dtd";> -<article id="bk_Quota"> - <title>ZooKeeper Quota's Guide</title> - <subtitle>A Guide to Deployment and Administration</subtitle> - <articleinfo> - <legalnotice> - <para> - Licensed under the Apache License, Version 2.0 (the "License"); you - may not use this file except in compliance with the License. You may - obtain a copy of the License at - <ulink url="http://www.apache.org/licenses/LICENSE-2.0";>http://www.apache.org/licenses/LICENSE-2.0 - </ulink> - . - </para> - <para>Unless required by applicable law or agreed to in - writing, software distributed under the License is distributed on an - "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either - express or implied. See the License for the specific language - governing permissions and limitations under the License.</para> - </legalnotice> - <abstract> - <para>This document contains information about deploying, - administering and mantaining ZooKeeper. It also discusses best - practices and common problems.</para> - </abstract> - </articleinfo> - <section id="zookeeper_quotas"> - <title>Quotas</title> - <para> ZooKeeper has both namespace and bytes quotas. You can use the ZooKeeperMain class to setup quotas. - ZooKeeper prints <emphasis>WARN</emphasis> messages if users exceed the quota assigned to them. The messages - are printed in the log of the ZooKeeper. - </para> - <para><computeroutput>$ bin/zkCli.sh -server host:port</computeroutput></para> - <para> The above command gives you a command line option of using quotas.</para> - <section> - <title>Setting Quotas</title> - <para>You can use - <emphasis>setquota</emphasis> to set a quota on a ZooKeeper node. It has an option of setting quota with - -n (for namespace) - and -b (for bytes). </para> - <para> The ZooKeeper quota are stored in ZooKeeper itself in /zookeeper/quota. To disable other people from - changing the quota's set the ACL for /zookeeper/quota such that only admins are able to read and write to it. - </para> - </section> - <section> - <title>Listing Quotas</title> - <para> You can use - <emphasis>listquota</emphasis> to list a quota on a ZooKeeper node. - </para> - </section> - <section> - <title> Deleting Quotas</title> - <para> You can use - <emphasis>delquota</emphasis> to delete quota on a ZooKeeper node. - </para> - </section> - </section> - </article>
http://git-wip-us.apache.org/repos/asf/zookeeper/blob/4607a3e1/src/docs/src/documentation/content/xdocs/zookeeperReconfig.xml ---------------------------------------------------------------------- diff --git a/src/docs/src/documentation/content/xdocs/zookeeperReconfig.xml b/src/docs/src/documentation/content/xdocs/zookeeperReconfig.xml deleted file mode 100644 index aa6419e..0000000 --- a/src/docs/src/documentation/content/xdocs/zookeeperReconfig.xml +++ /dev/null @@ -1,878 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> -<!-- - Copyright 2002-2004 The Apache Software Foundation - - Licensed under the Apache License, Version 2.0 (the "License"); - you may not use this file except in compliance with the License. - You may obtain a copy of the License at - - http://www.apache.org/licenses/LICENSE-2.0 - - Unless required by applicable law or agreed to in writing, software - distributed under the License is distributed on an "AS IS" BASIS, - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. - See the License for the specific language governing permissions and - limitations under the License. ---> -<!DOCTYPE article PUBLIC "-//OASIS//DTD Simplified DocBook XML V1.0//EN" -"http://www.oasis-open.org/docbook/xml/simple/1.0/sdocbook.dtd";> -<article id="ar_reconfig"> - <title>ZooKeeper Dynamic Reconfiguration</title> - - <articleinfo> - <legalnotice> - <para>Licensed under the Apache License, Version 2.0 (the "License"); - you may not use this file except in compliance with the License. You may - obtain a copy of the License at <ulink - url="http://www.apache.org/licenses/LICENSE-2.0";>http://www.apache.org/licenses/LICENSE-2.0</ulink>.</para> - - <para>Unless required by applicable law or agreed to in writing, - software distributed under the License is distributed on an "AS IS" - BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or - implied. See the License for the specific language governing permissions - and limitations under the License.</para> - </legalnotice> - - <abstract> - <para>This document contains information about Dynamic Reconfiguration in - ZooKeeper.</para> - </abstract> - </articleinfo> - <section id="ch_reconfig_intro"> - <title>Overview</title> - <para>Prior to the 3.5.0 release, the membership and all other configuration - parameters of Zookeeper were static - loaded during boot and immutable at - runtime. Operators resorted to ''rolling restarts'' - a manually intensive - and error-prone method of changing the configuration that has caused data - loss and inconsistency in production.</para> - <para>Starting with 3.5.0, ârolling restartsâ are no longer needed! - ZooKeeper comes with full support for automated configuration changes: the - set of Zookeeper servers, their roles (participant / observer), all ports, - and even the quorum system can be changed dynamically, without service - interruption and while maintaining data consistency. Reconfigurations are - performed immediately, just like other operations in ZooKeeper. Multiple - changes can be done using a single reconfiguration command. The dynamic - reconfiguration functionality does not limit operation concurrency, does - not require client operations to be stopped during reconfigurations, has a - very simple interface for administrators and no added complexity to other - client operations.</para> - <para>New client-side features allow clients to find out about configuration - changes and to update the connection string (list of servers and their - client ports) stored in their ZooKeeper handle. A probabilistic algorithm - is used to rebalance clients across the new configuration servers while - keeping the extent of client migrations proportional to the change in - ensemble membership.</para> - <para>This document provides the administrator manual for reconfiguration. - For a detailed description of the reconfiguration algorithms, performance - measurements, and more, please see our paper:</para> - <variablelist> - <varlistentry> - <term>Shraer, A., Reed, B., Malkhi, D., Junqueira, F. Dynamic - Reconfiguration of Primary/Backup Clusters. In <emphasis>USENIX Annual - Technical Conference (ATC) </emphasis>(2012), 425-437</term> - <listitem> - <para>Links: <ulink - url="https://www.usenix.org/system/files/conference/atc12/atc12-final74.pdf"; - >paper (pdf)</ulink>, <ulink - url="https://www.usenix.org/sites/default/files/conference/protected-files/shraer_atc12_slides.pdf"; - >slides (pdf)</ulink>, <ulink - url="https://www.usenix.org/conference/atc12/technical-sessions/presentation/shraer"; - >video</ulink>, <ulink - url="http://www.slideshare.net/Hadoop_Summit/dynamic-reconfiguration-of-zookeeper"; - >hadoop summit slides</ulink></para> - </listitem> - </varlistentry> - </variablelist> - <para><emphasis role="bold">Note:</emphasis> Starting with 3.5.3, the dynamic reconfiguration - feature is disabled by default, and has to be explicitly turned on via - <ulink url="zookeeperAdmin.html#sc_advancedConfiguration"> - reconfigEnabled </ulink> configuration option. - </para> - </section> - <section id="ch_reconfig_format"> - <title>Changes to Configuration Format</title> - <section id="sc_reconfig_clientport"> - <title>Specifying the client port</title> - <para>A client port of a server is the port on which the server accepts - client connection requests. Starting with 3.5.0 the - <emphasis>clientPort</emphasis> and <emphasis>clientPortAddress - </emphasis> configuration parameters should no longer be used. Instead, - this information is now part of the server keyword specification, which - becomes as follows:</para> - <para><computeroutput><![CDATA[server.<positive id> = <address1>:<port1>:<port2>[:role];[<client port address>:]<client port>]]></computeroutput></para> - <para>The client port specification is to the right of the semicolon. The - client port address is optional, and if not specified it defaults to - "0.0.0.0". As usual, role is also optional, it can be - <emphasis>participant</emphasis> or <emphasis>observer</emphasis> - (<emphasis>participant</emphasis> by default).</para> - <para> Examples of legal server statements: </para> - <itemizedlist> - <listitem> - <para><computeroutput>server.5 = 125.23.63.23:1234:1235;1236</computeroutput></para> - </listitem> - <listitem> - <para><computeroutput>server.5 = 125.23.63.23:1234:1235:participant;1236</computeroutput></para> - </listitem> - <listitem> - <para><computeroutput>server.5 = 125.23.63.23:1234:1235:observer;1236</computeroutput></para> - </listitem> - <listitem> - <para><computeroutput>server.5 = 125.23.63.23:1234:1235;125.23.63.24:1236</computeroutput></para> - </listitem> - <listitem> - <para><computeroutput>server.5 = 125.23.63.23:1234:1235:participant;125.23.63.23:1236</computeroutput></para> - </listitem> - </itemizedlist> - </section> - <section id="sc_reconfig_standaloneEnabled"> - <title>The <emphasis>standaloneEnabled</emphasis> flag</title> - <para>Prior to 3.5.0, one could run ZooKeeper in Standalone mode or in a - Distributed mode. These are separate implementation stacks, and - switching between them during run time is not possible. By default (for - backward compatibility) <emphasis>standaloneEnabled</emphasis> is set to - <emphasis>true</emphasis>. The consequence of using this default is that - if started with a single server the ensemble will not be allowed to - grow, and if started with more than one server it will not be allowed to - shrink to contain fewer than two participants.</para> - <para>Setting the flag to <emphasis>false</emphasis> instructs the system - to run the Distributed software stack even if there is only a single - participant in the ensemble. To achieve this the (static) configuration - file should contain:</para> - <para><computeroutput>standaloneEnabled=false</computeroutput></para> - <para>With this setting it is possible to start a ZooKeeper ensemble - containing a single participant and to dynamically grow it by adding - more servers. Similarly, it is possible to shrink an ensemble so that - just a single participant remains, by removing servers.</para> - <para>Since running the Distributed mode allows more flexibility, we - recommend setting the flag to <emphasis>false</emphasis>. We expect that - the legacy Standalone mode will be deprecated in the future.</para> - </section> - <section id="sc_reconfig_reconfigEnabled"> - <title>The <emphasis>reconfigEnabled</emphasis> flag</title> - <para>Starting with 3.5.0 and prior to 3.5.3, there is no way to disable - dynamic reconfiguration feature. We would like to offer the option of - disabling reconfiguration feature because with reconfiguration enabled, - we have a security concern that a malicious actor can make arbitrary changes - to the configuration of a ZooKeeper ensemble, including adding a compromised - server to the ensemble. We prefer to leave to the discretion of the user to - decide whether to enable it or not and make sure that the appropriate security - measure are in place. So in 3.5.3 the <ulink url="zookeeperAdmin.html#sc_advancedConfiguration"> - reconfigEnabled </ulink> configuration option is introduced - such that the reconfiguration feature can be completely disabled and any attempts - to reconfigure a cluster through reconfig API with or without authentication - will fail by default, unless <emphasis role="bold">reconfigEnabled</emphasis> is set to - <emphasis role="bold">true</emphasis>. - </para> - <para>To set the option to true, the configuration file (zoo.cfg) should contain:</para> - <para><computeroutput>reconfigEnabled=true</computeroutput></para> - </section> - <section id="sc_reconfig_file"> - <title>Dynamic configuration file</title> - <para>Starting with 3.5.0 we're distinguishing between dynamic - configuration parameters, which can be changed during runtime, and - static configuration parameters, which are read from a configuration - file when a server boots and don't change during its execution. For now, - the following configuration keywords are considered part of the dynamic - configuration: <emphasis>server</emphasis>, <emphasis>group</emphasis> - and <emphasis>weight</emphasis>.</para> - <para>Dynamic configuration parameters are stored in a separate file on - the server (which we call the dynamic configuration file). This file is - linked from the static config file using the new - <emphasis>dynamicConfigFile</emphasis> keyword.</para> - <para><emphasis role="bold">Example</emphasis></para> - <example> - <title>zoo_replicated1.cfg</title> - <programlisting>tickTime=2000 -dataDir=/zookeeper/data/zookeeper1 -initLimit=5 -syncLimit=2 -dynamicConfigFile=/zookeeper/conf/zoo_replicated1.cfg.dynamic</programlisting> - </example> - <example> - <title>zoo_replicated1.cfg.dynamic</title> - <programlisting>server.1=125.23.63.23:2780:2783:participant;2791 -server.2=125.23.63.24:2781:2784:participant;2792 -server.3=125.23.63.25:2782:2785:participant;2793</programlisting> - </example> - <para>When the ensemble configuration changes, the static configuration - parameters remain the same. The dynamic parameters are pushed by - ZooKeeper and overwrite the dynamic configuration files on all servers. - Thus, the dynamic configuration files on the different servers are - usually identical (they can only differ momentarily when a - reconfiguration is in progress, or if a new configuration hasn't - propagated yet to some of the servers). Once created, the dynamic - configuration file should not be manually altered. Changed are only made - through the new reconfiguration commands outlined below. Note that - changing the config of an offline cluster could result in an - inconsistency with respect to configuration information stored in the - ZooKeeper log (and the special configuration znode, populated from the - log) and is therefore highly discouraged.</para> - <para><emphasis role="bold">Example 2</emphasis></para> - <para>Users may prefer to initially specify a single configuration file. - The following is thus also legal:</para> - <example> - <title>zoo_replicated1.cfg</title> - <programlisting>tickTime=2000 -dataDir=/zookeeper/data/zookeeper1 -initLimit=5 -syncLimit=2 -clientPort=<emphasis role="bold">2791</emphasis> // note that this line is now redundant and therefore not recommended -server.1=125.23.63.23:2780:2783:participant;<emphasis role="bold">2791</emphasis> -server.2=125.23.63.24:2781:2784:participant;2792 -server.3=125.23.63.25:2782:2785:participant;2793</programlisting> - </example> - <para>The configuration files on each server will be automatically split - into dynamic and static files, if they are not already in this format. - So the configuration file above will be automatically transformed into - the two files in Example 1. Note that the clientPort and - clientPortAddress lines (if specified) will be automatically removed - during this process, if they are redundant (as in the example above). - The original static configuration file is backed up (in a .bak - file).</para> - </section> - <section id="sc_reconfig_backward"> - <title>Backward compatibility</title> - <para>We still support the old configuration format. For example, the - following configuration file is acceptable (but not recommended):</para> - <example> - <title>zoo_replicated1.cfg</title> - <programlisting>tickTime=2000 -dataDir=/zookeeper/data/zookeeper1 -initLimit=5 -syncLimit=2 -clientPort=2791 -server.1=125.23.63.23:2780:2783:participant -server.2=125.23.63.24:2781:2784:participant -server.3=125.23.63.25:2782:2785:participant</programlisting> - </example> - <para>During boot, a dynamic configuration file is created and contains - the dynamic part of the configuration as explained earlier. In this - case, however, the line "clientPort=2791" will remain in the static - configuration file of server 1 since it is not redundant -- it was not - specified as part of the "server.1=..." using the format explained in - the section <xref linkend="ch_reconfig_format"/>. If a reconfiguration - is invoked that sets the client port of server 1, we remove - "clientPort=2791" from the static configuration file (the dynamic file - now contain this information as part of the specification of server - 1).</para> - </section> - </section> - <section id="ch_reconfig_upgrade"> - <title>Upgrading to 3.5.0</title> - <para>Upgrading a running ZooKeeper ensemble to 3.5.0 should be done only - after upgrading your ensemble to the 3.4.6 release. Note that this is only - necessary for rolling upgrades (if you're fine with shutting down the - system completely, you don't have to go through 3.4.6). If you attempt a - rolling upgrade without going through 3.4.6 (for example from 3.4.5), you - may get the following error:</para> - <programlisting>2013-01-30 11:32:10,663 [myid:2] - INFO [localhost/127.0.0.1:2784:QuorumCnxManager$Listener@498] - Received connection request /127.0.0.1:60876 -2013-01-30 11:32:10,663 [myid:2] - WARN [localhost/127.0.0.1:2784:QuorumCnxManager@349] - Invalid server id: -65536</programlisting> - <para>During a rolling upgrade, each server is taken down in turn and - rebooted with the new 3.5.0 binaries. Before starting the server with - 3.5.0 binaries, we highly recommend updating the configuration file so - that all server statements "server.x=..." contain client ports (see the - section <xref linkend="sc_reconfig_clientport"/>). As explained earlier - you may leave the configuration in a single file, as well as leave the - clientPort/clientPortAddress statements (although if you specify client - ports in the new format, these statements are now redundant).</para> - </section> - - <section id="ch_reconfig_dyn"> - <title>Dynamic Reconfiguration of the ZooKeeper Ensemble</title> - <para>The ZooKeeper Java and C API were extended with getConfig and reconfig - commands that facilitate reconfiguration. Both commands have a synchronous - (blocking) variant and an asynchronous one. We demonstrate these commands - here using the Java CLI, but note that you can similarly use the C CLI or - invoke the commands directly from a program just like any other ZooKeeper - command.</para> - - <section id="ch_reconfig_api"> - <title>API</title> - <para>There are two sets of APIs for both Java and C client. - </para> - <variablelist> - <varlistentry> - <term><emphasis role="bold">Reconfiguration API</emphasis></term> - - <listitem> - <para>Reconfiguration API is used to reconfigure the ZooKeeper cluster. - Starting with 3.5.3, reconfiguration Java APIs are moved into ZooKeeperAdmin class - from ZooKeeper class, and use of this API requires ACL setup and user - authentication (see <xref linkend="sc_reconfig_access_control"/> for more information.). - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><emphasis role="bold">Get Configuration API</emphasis></term> - <listitem> - <para>Get configuration APIs are used to retrieve ZooKeeper cluster configuration information - stored in /zookeeper/config znode. Use of this API does not require specific setup or authentication, - because /zookeeper/config is readable to any users.</para> - </listitem> - </varlistentry> - </variablelist> - </section> - - <section id="sc_reconfig_access_control"> - <title>Security</title> - <para>Prior to <emphasis role="bold">3.5.3</emphasis>, there is no enforced security mechanism - over reconfig so any ZooKeeper clients that can connect to ZooKeeper server ensemble - will have the ability to change the state of a ZooKeeper cluster via reconfig. - It is thus possible for a malicious client to add compromised server to an ensemble, - e.g., add a compromised server, or remove legitimate servers. - Cases like these could be security vulnerabilities on a case by case basis. - </para> - <para>To address this security concern, we introduced access control over reconfig - starting from <emphasis role="bold">3.5.3</emphasis> such that only a specific set of users - can use reconfig commands or APIs, and these users need be configured explicitly. In addition, - the setup of ZooKeeper cluster must enable authentication so ZooKeeper clients can be authenticated. - </para> - <para> - We also provides an escape hatch for users who operate and interact with a ZooKeeper ensemble in a secured - environment (i.e. behind company firewall). For those users who want to use reconfiguration feature but - don't want the overhead of configuring an explicit list of authorized user for reconfig access checks, - they can set <ulink url="zookeeperAdmin.html#sc_authOptions">"skipACL"</ulink> to "yes" which will - skip ACL check and allow any user to reconfigure cluster. - </para> - <para> - Overall, ZooKeeper provides flexible configuration options for the reconfigure feature - that allow a user to choose based on user's security requirement. - We leave to the discretion of the user to decide appropriate security measure are in place. - </para> - <variablelist> - <varlistentry> - <term><emphasis role="bold">Access Control</emphasis></term> - - <listitem> - <para>The dynamic configuration is stored in a special znode - ZooDefs.CONFIG_NODE = /zookeeper/config. This node by default is read only - for all users, except super user and users that's explicitly configured for write - access. - </para> - - <para>Clients that need to use reconfig commands or reconfig API should be configured as users - that have write access to CONFIG_NODE. By default, only the super user has full control including - write access to CONFIG_NODE. Additional users can be granted write access through superuser - by setting an ACL that has write permission associated with specified user. - </para> - - <para>A few examples of how to setup ACLs and use reconfiguration API with authentication can be found in - ReconfigExceptionTest.java and TestReconfigServer.cc.</para> - </listitem> - </varlistentry> - - <varlistentry> - <term><emphasis role="bold">Authentication</emphasis></term> - - <listitem> - <para>Authentication of users is orthogonal to the access control and is delegated to - existing authentication mechanism supported by ZooKeeper's pluggable authentication schemes. - See <ulink - url="https://cwiki.apache.org/confluence/display/ZOOKEEPER/Zookeeper+and+SASL"; - >ZooKeeper and SASL</ulink> for more details on this topic. - </para> - </listitem> - </varlistentry> - - <varlistentry> - <term><emphasis role="bold">Disable ACL check</emphasis></term> - <listitem> - <para> - ZooKeeper supports <ulink - url="zookeeperAdmin.html#sc_authOptions">"skipACL"</ulink> option such that ACL - check will be completely skipped, if skipACL is set to "yes". In such cases any unauthenticated - users can use reconfig API. - </para> - </listitem> - </varlistentry> - </variablelist> - </section> - - <section id="sc_reconfig_retrieving"> - <title>Retrieving the current dynamic configuration</title> - <para>The dynamic configuration is stored in a special znode - ZooDefs.CONFIG_NODE = /zookeeper/config. The new - <command>config</command> CLI command reads this znode (currently it is - simply a wrapper to <command>get /zookeeper/config</command>). As with - normal reads, to retrieve the latest committed value you should do a - <command>sync</command> first.</para> - <programlisting>[zk: 127.0.0.1:2791(CONNECTED) 3] config -server.1=localhost:2780:2783:participant;localhost:2791 -server.2=localhost:2781:2784:participant;localhost:2792 -server.3=localhost:2782:2785:participant;localhost:2793 -<emphasis role="bold">version=400000003</emphasis></programlisting> - <para>Notice the last line of the output. This is the configuration - version. The version equals to the zxid of the reconfiguration command - which created this configuration. The version of the first established - configuration equals to the zxid of the NEWLEADER message sent by the - first successfully established leader. When a configuration is written - to a dynamic configuration file, the version automatically becomes part - of the filename and the static configuration file is updated with the - path to the new dynamic configuration file. Configuration files - corresponding to earlier versions are retained for backup - purposes.</para> - <para>During boot time the version (if it exists) is extracted from the - filename. The version should never be altered manually by users or the - system administrator. It is used by the system to know which - configuration is most up-to-date. Manipulating it manually can result in - data loss and inconsistency.</para> - <para>Just like a <command>get</command> command, the - <command>config</command> CLI command accepts the <option>-w</option> - flag for setting a watch on the znode, and <option>-s</option> flag for - displaying the Stats of the znode. It additionally accepts a new flag - <option>-c</option> which outputs only the version and the client - connection string corresponding to the current configuration. For - example, for the configuration above we would get:</para> - <programlisting>[zk: 127.0.0.1:2791(CONNECTED) 17] config -c -400000003 localhost:2791,localhost:2793,localhost:2792</programlisting> - <para>Note that when using the API directly, this command is called - <command>getConfig</command>.</para> - <para>As any read command it returns the configuration known to the - follower to which your client is connected, which may be slightly - out-of-date. One can use the <command>sync</command> command for - stronger guarantees. For example using the Java API:</para> - <programlisting>zk.sync(ZooDefs.CONFIG_NODE, void_callback, context); -zk.getConfig(watcher, callback, context);</programlisting> - <para>Note: in 3.5.0 it doesn't really matter which path is passed to the - <command>sync() </command> command as all the server's state is brought - up to date with the leader (so one could use a different path instead of - ZooDefs.CONFIG_NODE). However, this may change in the future.</para> - </section> - <section id="sc_reconfig_modifying"> - <title>Modifying the current dynamic configuration</title> - <para>Modifying the configuration is done through the - <command>reconfig</command> command. There are two modes of - reconfiguration: incremental and non-incremental (bulk). The - non-incremental simply specifies the new dynamic configuration of the - system. The incremental specifies changes to the current configuration. - The <command>reconfig</command> command returns the new - configuration.</para> - <para>A few examples are in: <filename>ReconfigTest.java</filename>, - <filename>ReconfigRecoveryTest.java</filename> and - <filename>TestReconfigServer.cc</filename>.</para> - <section id="sc_reconfig_general"> - <title>General</title> - <para><emphasis role="bold">Removing servers:</emphasis> Any server can - be removed, including the leader (although removing the leader will - result in a short unavailability, see Figures 6 and 8 in the <ulink - url="https://www.usenix.org/conference/usenixfederatedconferencesweek/dynamic-recon%EF%AC%81guration-primarybackup-clusters"; - >paper</ulink>). The server will not be shut-down automatically. - Instead, it becomes a "non-voting follower". This is somewhat similar - to an observer in that its votes don't count towards the Quorum of - votes necessary to commit operations. However, unlike a non-voting - follower, an observer doesn't actually see any operation proposals and - does not ACK them. Thus a non-voting follower has a more significant - negative effect on system throughput compared to an observer. - Non-voting follower mode should only be used as a temporary mode, - before shutting the server down, or adding it as a follower or as an - observer to the ensemble. We do not shut the server down automatically - for two main reasons. The first reason is that we do not want all the - clients connected to this server to be immediately disconnected, - causing a flood of connection requests to other servers. Instead, it - is better if each client decides when to migrate independently. The - second reason is that removing a server may sometimes (rarely) be - necessary in order to change it from "observer" to "participant" (this - is explained in the section <xref linkend="sc_reconfig_additional" - />).</para> - <para>Note that the new configuration should have some minimal number of - participants in order to be considered legal. If the proposed change - would leave the cluster with less than 2 participants and standalone - mode is enabled (standaloneEnabled=true, see the section <xref - linkend="sc_reconfig_standaloneEnabled"/>), the reconfig will not be - processed (BadArgumentsException). If standalone mode is disabled - (standaloneEnabled=false) then its legal to remain with 1 or more - participants.</para> - <para><emphasis role="bold">Adding servers:</emphasis> Before a - reconfiguration is invoked, the administrator must make sure that a - quorum (majority) of participants from the new configuration are - already connected and synced with the current leader. To achieve this - we need to connect a new joining server to the leader before it is - officially part of the ensemble. This is done by starting the joining - server using an initial list of servers which is technically not a - legal configuration of the system but (a) contains the joiner, and (b) - gives sufficient information to the joiner in order for it to find and - connect to the current leader. We list a few different options of - doing this safely.</para> - <orderedlist> - <listitem> - <para>Initial configuration of joiners is comprised of servers in - the last committed configuration and one or more joiners, where - <emphasis role="bold">joiners are listed as observers.</emphasis> - For example, if servers D and E are added at the same time to (A, - B, C) and server C is being removed, the initial configuration of - D could be (A, B, C, D) or (A, B, C, D, E), where D and E are - listed as observers. Similarly, the configuration of E could be - (A, B, C, E) or (A, B, C, D, E), where D and E are listed as - observers. <emphasis role="bold">Note that listing the joiners as - observers will not actually make them observers - it will only - prevent them from accidentally forming a quorum with other - joiners.</emphasis> Instead, they will contact the servers in the - current configuration and adopt the last committed configuration - (A, B, C), where the joiners are absent. Configuration files of - joiners are backed up and replaced automatically as this happens. - After connecting to the current leader, joiners become non-voting - followers until the system is reconfigured and they are added to - the ensemble (as participant or observer, as appropriate).</para> - </listitem> - <listitem> - <para>Initial configuration of each joiner is comprised of servers - in the last committed configuration + <emphasis role="bold">the - joiner itself, listed as a participant.</emphasis> For example, to - add a new server D to a configuration consisting of servers (A, B, - C), the administrator can start D using an initial configuration - file consisting of servers (A, B, C, D). If both D and E are added - at the same time to (A, B, C), the initial configuration of D - could be (A, B, C, D) and the configuration of E could be (A, B, - C, E). Similarly, if D is added and C is removed at the same time, - the initial configuration of D could be (A, B, C, D). Never list - more than one joiner as participant in the initial configuration - (see warning below).</para> - </listitem> - <listitem> - <para>Whether listing the joiner as an observer or as participant, - it is also fine not to list all the current configuration servers, - as long as the current leader is in the list. For example, when - adding D we could start D with a configuration file consisting of - just (A, D) if A is the current leader. however this is more - fragile since if A fails before D officially joins the ensemble, D - doesnât know anyone else and therefore the administrator will have - to intervene and restart D with another server list.</para> - </listitem> - </orderedlist> - <note> - <title>Warning</title> - <para>Never specify more than one joining server in the same initial - configuration as participants. Currently, the joining servers donât - know that they are joining an existing ensemble; if multiple joiners - are listed as participants they may form an independent quorum - creating a split-brain situation such as processing operations - independently from your main ensemble. It is OK to list multiple - joiners as observers in an initial config.</para> - </note> - <para>If the configuration of existing servers changes or they become unavailable - before the joiner succeeds to connect and learn obout configuration changes, the - joiner may need to be restarted with an updated configuration file in order to be - able to connect.</para> - <para>Finally, note that once connected to the leader, a joiner adopts - the last committed configuration, in which it is absent (the initial - config of the joiner is backed up before being rewritten). If the - joiner restarts in this state, it will not be able to boot since it is - absent from its configuration file. In order to start it youâll once - again have to specify an initial configuration.</para> - <para><emphasis role="bold">Modifying server parameters:</emphasis> One - can modify any of the ports of a server, or its role - (participant/observer) by adding it to the ensemble with different - parameters. This works in both the incremental and the bulk - reconfiguration modes. It is not necessary to remove the server and - then add it back; just specify the new parameters as if the server is - not yet in the system. The server will detect the configuration change - and perform the necessary adjustments. See an example in the section - <xref linkend="sc_reconfig_incremental"/> and an exception to this - rule in the section <xref linkend="sc_reconfig_additional"/>.</para> - <para>It is also possible to change the Quorum System used by the - ensemble (for example, change the Majority Quorum System to a - Hierarchical Quorum System on the fly). This, however, is only allowed - using the bulk (non-incremental) reconfiguration mode. In general, - incremental reconfiguration only works with the Majority Quorum - System. Bulk reconfiguration works with both Hierarchical and Majority - Quorum Systems.</para> - <para><emphasis role="bold">Performance Impact:</emphasis> There is - practically no performance impact when removing a follower, since it - is not being automatically shut down (the effect of removal is that - the server's votes are no longer being counted). When adding a server, - there is no leader change and no noticeable performance disruption. - For details and graphs please see Figures 6, 7 and 8 in the <ulink - url="https://www.usenix.org/conference/usenixfederatedconferencesweek/dynamic-recon%EF%AC%81guration-primarybackup-clusters"; - >paper</ulink>.</para> - <para>The most significant disruption will happen when a leader change - is caused, in one of the following cases:</para> - <orderedlist> - <listitem> - <para>Leader is removed from the ensemble.</para> - </listitem> - <listitem> - <para>Leader's role is changed from participant to observer.</para> - </listitem> - <listitem> - <para>The port used by the leader to send transactions to others - (quorum port) is modified.</para> - </listitem> - </orderedlist> - <para>In these cases we perform a leader hand-off where the old leader - nominates a new leader. The resulting unavailability is usually - shorter than when a leader crashes since detecting leader failure is - unnecessary and electing a new leader can usually be avoided during a - hand-off (see Figures 6 and 8 in the <ulink - url="https://www.usenix.org/conference/usenixfederatedconferencesweek/dynamic-recon%EF%AC%81guration-primarybackup-clusters"; - >paper</ulink>).</para> - <para>When the client port of a server is modified, it does not drop - existing client connections. New connections to the server will have - to use the new client port.</para> - <para><emphasis role="bold">Progress guarantees:</emphasis> Up to the - invocation of the reconfig operation, a quorum of the old - configuration is required to be available and connected for ZooKeeper - to be able to make progress. Once reconfig is invoked, a quorum of - both the old and of the new configurations must be available. The - final transition happens once (a) the new configuration is activated, - and (b) all operations scheduled before the new configuration is - activated by the leader are committed. Once (a) and (b) happen, only a - quorum of the new configuration is required. Note, however, that - neither (a) nor (b) are visible to a client. Specifically, when a - reconfiguration operation commits, it only means that an activation - message was sent out by the leader. It does not necessarily mean that - a quorum of the new configuration got this message (which is required - in order to activate it) or that (b) has happened. If one wants to - make sure that both (a) and (b) has already occurred (for example, in - order to know that it is safe to shut down old servers that were - removed), one can simply invoke an update - (<command>set-data</command>, or some other quorum operation, but not - a <command>sync</command>) and wait for it to commit. An alternative - way to achieve this was to introduce another round to the - reconfiguration protocol (which, for simplicity and compatibility with - Zab, we decided to avoid).</para> - </section> - <section id="sc_reconfig_incremental"> - <title>Incremental mode</title> - <para>The incremental mode allows adding and removing servers to the - current configuration. Multiple changes are allowed. For - example:</para> - <para><userinput>> reconfig -remove 3 -add - server.5=125.23.63.23:1234:1235;1236</userinput></para> - <para>Both the add and the remove options get a list of comma separated - arguments (no spaces):</para> - <para><userinput>> reconfig -remove 3,4 -add - server.5=localhost:2111:2112;2113,6=localhost:2114:2115:observer;2116</userinput></para> - <para>The format of the server statement is exactly the same as - described in the section <xref linkend="sc_reconfig_clientport"/> and - includes the client port. Notice that here instead of "server.5=" you - can just say "5=". In the example above, if server 5 is already in the - system, but has different ports or is not an observer, it is updated - and once the configuration commits becomes an observer and starts - using these new ports. This is an easy way to turn participants into - observers and vise versa or change any of their ports, without - rebooting the server.</para> - <para>ZooKeeper supports two types of Quorum Systems â the simple - Majority system (where the leader commits operations after receiving - ACKs from a majority of voters) and a more complex Hierarchical - system, where votes of different servers have different weights and - servers are divided into voting groups. Currently, incremental - reconfiguration is allowed only if the last proposed configuration - known to the leader uses a Majority Quorum System - (BadArgumentsException is thrown otherwise).</para> - <para>Incremental mode - examples using the Java API:</para> - <programlisting><![CDATA[List<String> leavingServers = new ArrayList<String>(); -leavingServers.add("1"); -leavingServers.add("2"); -byte[] config = zk.reconfig(null, leavingServers, null, -1, new Stat());]]></programlisting> - - <programlisting><![CDATA[List<String> leavingServers = new ArrayList<String>(); -List<String> joiningServers = new ArrayList<String>(); -leavingServers.add("1"); -joiningServers.add("server.4=localhost:1234:1235;1236"); -byte[] config = zk.reconfig(joiningServers, leavingServers, null, -1, new Stat()); - -String configStr = new String(config); -System.out.println(configStr);]]></programlisting> - <para>There is also an asynchronous API, and an API accepting comma - separated Strings instead of List<String>. See - src/java/main/org/apache/zookeeper/ZooKeeper.java.</para> - </section> - <section id="sc_reconfig_nonincremental"> - <title>Non-incremental mode</title> - <para>The second mode of reconfiguration is non-incremental, whereby a - client gives a complete specification of the new dynamic system - configuration. The new configuration can either be given in place or - read from a file:</para> - <para><userinput>> reconfig -file newconfig.cfg - </userinput>//newconfig.cfg is a dynamic config file, see <xref - linkend="sc_reconfig_file"/></para> - <para><userinput>> reconfig -members - server.1=125.23.63.23:2780:2783:participant;2791,server.2=125.23.63.24:2781:2784:participant;2792,server.3=125.23.63.25:2782:2785:participant;2793</userinput></para> - <para>The new configuration may use a different Quorum System. For - example, you may specify a Hierarchical Quorum System even if the - current ensemble uses a Majority Quorum System.</para> - <para>Bulk mode - example using the Java API:</para> - <programlisting><![CDATA[List<String> newMembers = new ArrayList<String>(); -newMembers.add("server.1=1111:1234:1235;1236"); -newMembers.add("server.2=1112:1237:1238;1239"); -newMembers.add("server.3=1114:1240:1241:observer;1242"); - -byte[] config = zk.reconfig(null, null, newMembers, -1, new Stat()); - -String configStr = new String(config); -System.out.println(configStr);]]></programlisting> - <para>There is also an asynchronous API, and an API accepting comma - separated String containing the new members instead of - List<String>. See - src/java/main/org/apache/zookeeper/ZooKeeper.java.</para> - </section> - <section id="sc_reconfig_conditional"> - <title>Conditional reconfig</title> - <para>Sometimes (especially in non-incremental mode) a new proposed - configuration depends on what the client "believes" to be the current - configuration, and should be applied only to that configuration. - Specifically, the <command>reconfig</command> succeeds only if the - last configuration at the leader has the specified version.</para> - <para><userinput><![CDATA[> reconfig -file <filename> -v <version>]]></userinput></para> - <para>In the previously listed Java examples, instead of -1 one could - specify a configuration version to condition the - reconfiguration.</para> - </section> - <section id="sc_reconfig_errors"> - <title>Error conditions</title> - <para>In addition to normal ZooKeeper error conditions, a - reconfiguration may fail for the following reasons:</para> - <orderedlist> - <listitem> - <para>another reconfig is currently in progress - (ReconfigInProgress)</para> - </listitem> - <listitem> - <para>the proposed change would leave the cluster with less than 2 - participants, in case standalone mode is enabled, or, if - standalone mode is disabled then its legal to remain with 1 or - more participants (BadArgumentsException)</para> - </listitem> - <listitem> - <para>no quorum of the new configuration was connected and - up-to-date with the leader when the reconfiguration processing - began (NewConfigNoQuorum)</para> - </listitem> - <listitem> - <para><userinput>-v x</userinput> was specified, but the version - <userinput>y</userinput> of the latest configuration is not - <userinput>x</userinput> (BadVersionException)</para> - </listitem> - <listitem> - <para>an incremental reconfiguration was requested but the last - configuration at the leader uses a Quorum System which is - different from the Majority system (BadArgumentsException)</para> - </listitem> - <listitem> - <para>syntax error (BadArgumentsException)</para> - </listitem> - <listitem> - <para>I/O exception when reading the configuration from a file - (BadArgumentsException)</para> - </listitem> - </orderedlist> - <para>Most of these are illustrated by test-cases in - <filename>ReconfigFailureCases.java</filename>.</para> - </section> - <section id="sc_reconfig_additional"> - <title>Additional comments</title> - <para><emphasis role="bold">Liveness:</emphasis> To better understand - the difference between incremental and non-incremental - reconfiguration, suppose that client C1 adds server D to the system - while a different client C2 adds server E. With the non-incremental - mode, each client would first invoke <command>config</command> to find - out the current configuration, and then locally create a new list of - servers by adding its own suggested server. The new configuration can - then be submitted using the non-incremental - <command>reconfig</command> command. After both reconfigurations - complete, only one of E or D will be added (not both), depending on - which client's request arrives second to the leader, overwriting the - previous configuration. The other client can repeat the process until - its change takes effect. This method guarantees system-wide progress - (i.e., for one of the clients), but does not ensure that every client - succeeds. To have more control C2 may request to only execute the - reconfiguration in case the version of the current configuration - hasn't changed, as explained in the section <xref - linkend="sc_reconfig_conditional"/>. In this way it may avoid blindly - overwriting the configuration of C1 if C1's configuration reached the - leader first.</para> - <para>With incremental reconfiguration, both changes will take effect as - they are simply applied by the leader one after the other to the - current configuration, whatever that is (assuming that the second - reconfig request reaches the leader after it sends a commit message - for the first reconfig request -- currently the leader will refuse to - propose a reconfiguration if another one is already pending). Since - both clients are guaranteed to make progress, this method guarantees - stronger liveness. In practice, multiple concurrent reconfigurations - are probably rare. Non-incremental reconfiguration is currently the - only way to dynamically change the Quorum System. Incremental - configuration is currently only allowed with the Majority Quorum - System.</para> - <para><emphasis role="bold">Changing an observer into a - follower:</emphasis> Clearly, changing a server that participates in - voting into an observer may fail if error (2) occurs, i.e., if fewer - than the minimal allowed number of participants would remain. However, - converting an observer into a participant may sometimes fail for a - more subtle reason: Suppose, for example, that the current - configuration is (A, B, C, D), where A is the leader, B and C are - followers and D is an observer. In addition, suppose that B has - crashed. If a reconfiguration is submitted where D is said to become a - follower, it will fail with error (3) since in this configuration, a - majority of voters in the new configuration (any 3 voters), must be - connected and up-to-date with the leader. An observer cannot - acknowledge the history prefix sent during reconfiguration, and - therefore it does not count towards these 3 required servers and the - reconfiguration will be aborted. In case this happens, a client can - achieve the same task by two reconfig commands: first invoke a - reconfig to remove D from the configuration and then invoke a second - command to add it back as a participant (follower). During the - intermediate state D is a non-voting follower and can ACK the state - transfer performed during the second reconfig comand.</para> - </section> - </section> - </section> - <section id="ch_reconfig_rebalancing"> - <title>Rebalancing Client Connections</title> - <para>When a ZooKeeper cluster is started, if each client is given the same - connection string (list of servers), the client will randomly choose a - server in the list to connect to, which makes the expected number of - client connections per server the same for each of the servers. We - implemented a method that preserves this property when the set of servers - changes through reconfiguration. See Sections 4 and 5.1 in the <ulink - url="https://www.usenix.org/conference/usenixfederatedconferencesweek/dynamic-recon%EF%AC%81guration-primarybackup-clusters"; - >paper</ulink>.</para> - <para>In order for the method to work, all clients must subscribe to - configuration changes (by setting a watch on /zookeeper/config either - directly or through the <command>getConfig</command> API command). When - the watch is triggered, the client should read the new configuration by - invoking <command>sync</command> and <command>getConfig</command> and if - the configuration is indeed new invoke the - <command>updateServerList</command> API command. To avoid mass client - migration at the same time, it is better to have each client sleep a - random short period of time before invoking - <command>updateServerList</command>.</para> - <para>A few examples can be found in: - <filename>StaticHostProviderTest.java</filename> and - <filename>TestReconfig.cc</filename></para> - <para>Example (this is not a recipe, but a simplified example just to - explain the general idea):</para> - <programlisting><![CDATA[ -public void process(WatchedEvent event) { - synchronized (this) { - if (event.getType() == EventType.None) { - connected = (event.getState() == KeeperState.SyncConnected); - notifyAll(); - } else if (event.getPath()!=null && event.getPath().equals(ZooDefs.CONFIG_NODE)) { - // in prod code never block the event thread! - zk.sync(ZooDefs.CONFIG_NODE, this, null); - zk.getConfig(this, this, null); - } - } -} -public void processResult(int rc, String path, Object ctx, byte[] data, Stat stat) { - if (path!=null && path.equals(ZooDefs.CONFIG_NODE)) { - String config[] = ConfigUtils.getClientConfigStr(new String(data)).split(" "); // similar to config -c - long version = Long.parseLong(config[0], 16); - if (this.configVersion == null){ - this.configVersion = version; - } else if (version > this.configVersion) { - hostList = config[1]; - try { - // the following command is not blocking but may cause the client to close the socket and - // migrate to a different server. In practice its better to wait a short period of time, chosen - // randomly, so that different clients migrate at different times - zk.updateServerList(hostList); - } catch (IOException e) { - System.err.println("Error updating server list"); - e.printStackTrace(); - } - this.configVersion = version; -} } }]]></programlisting> - </section> -</article> http://git-wip-us.apache.org/repos/asf/zookeeper/blob/4607a3e1/src/docs/src/documentation/content/xdocs/zookeeperStarted.xml ---------------------------------------------------------------------- diff --git a/src/docs/src/documentation/content/xdocs/zookeeperStarted.xml b/src/docs/src/documentation/content/xdocs/zookeeperStarted.xml deleted file mode 100644 index e5cd777..0000000 --- a/src/docs/src/documentation/content/xdocs/zookeeperStarted.xml +++ /dev/null @@ -1,419 +0,0 @@ -<?xml version="1.0" encoding="UTF-8"?> -<!-- - Copyright 2002-2004 The Apache Software Foundation - - Licensed under the Apache License, Version 2.0 (the "License"); - you may not use this file except in compliance with the License. - You may obtain a copy of the License at - - http://www.apache.org/licenses/LICENSE-2.0 - - Unless required by applicable law or agreed to in writing, software - distributed under the License is distributed on an "AS IS" BASIS, - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. - See the License for the specific language governing permissions and - limitations under the License. ---> - -<!DOCTYPE article PUBLIC "-//OASIS//DTD Simplified DocBook XML V1.0//EN" -"http://www.oasis-open.org/docbook/xml/simple/1.0/sdocbook.dtd";> -<article id="bk_GettStartedGuide"> - <title>ZooKeeper Getting Started Guide</title> - - <articleinfo> - <legalnotice> - <para>Licensed under the Apache License, Version 2.0 (the "License"); - you may not use this file except in compliance with the License. You may - obtain a copy of the License at <ulink - url="http://www.apache.org/licenses/LICENSE-2.0";>http://www.apache.org/licenses/LICENSE-2.0</ulink>.</para> - - <para>Unless required by applicable law or agreed to in writing, - software distributed under the License is distributed on an "AS IS" - BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or - implied. See the License for the specific language governing permissions - and limitations under the License.</para> - </legalnotice> - - <abstract> - <para>This guide contains detailed information about creating - distributed applications that use ZooKeeper. It discusses the basic - operations ZooKeeper supports, and how these can be used to build - higher-level abstractions. It contains solutions to common tasks, a - troubleshooting guide, and links to other information.</para> - </abstract> - </articleinfo> - - <section id="ch_GettingStarted"> - <title>Getting Started: Coordinating Distributed Applications with - ZooKeeper</title> - - <para>This document contains information to get you started quickly with - ZooKeeper. It is aimed primarily at developers hoping to try it out, and - contains simple installation instructions for a single ZooKeeper server, a - few commands to verify that it is running, and a simple programming - example. Finally, as a convenience, there are a few sections regarding - more complicated installations, for example running replicated - deployments, and optimizing the transaction log. However for the complete - instructions for commercial deployments, please refer to the <ulink - url="zookeeperAdmin.html">ZooKeeper - Administrator's Guide</ulink>.</para> - - <section id="sc_Prerequisites"> - <title>Pre-requisites</title> - - <para>See <ulink url="zookeeperAdmin.html#sc_systemReq"> - System Requirements</ulink> in the Admin guide.</para> - </section> - - <section id="sc_Download"> - <title>Download</title> - - <para>To get a ZooKeeper distribution, download a recent - <ulink url="http://zookeeper.apache.org/releases.html";> - stable</ulink> release from one of the Apache Download - Mirrors.</para> - </section> - - <section id="sc_InstallingSingleMode"> - <title>Standalone Operation</title> - - <para>Setting up a ZooKeeper server in standalone mode is - straightforward. The server is contained in a single JAR file, - so installation consists of creating a configuration.</para> - - <para>Once you've downloaded a stable ZooKeeper release unpack - it and cd to the root</para> - - <para>To start ZooKeeper you need a configuration file. Here is a sample, - create it in <emphasis role="bold">conf/zoo.cfg</emphasis>:</para> - -<programlisting> -tickTime=2000 -dataDir=/var/lib/zookeeper -clientPort=2181 -</programlisting> - - <para>This file can be called anything, but for the sake of this - discussion call - it <emphasis role="bold">conf/zoo.cfg</emphasis>. Change the - value of <emphasis role="bold">dataDir</emphasis> to specify an - existing (empty to start with) directory. Here are the meanings - for each of the fields:</para> - - <variablelist> - <varlistentry> - <term><emphasis role="bold">tickTime</emphasis></term> - - <listitem> - <para>the basic time unit in milliseconds used by ZooKeeper. It is - used to do heartbeats and the minimum session timeout will be - twice the tickTime.</para> - </listitem> - </varlistentry> - </variablelist> - - <variablelist> - <varlistentry> - <term><emphasis role="bold">dataDir</emphasis></term> - - <listitem> - <para>the location to store the in-memory database snapshots and, - unless specified otherwise, the transaction log of updates to the - database.</para> - </listitem> - </varlistentry> - - <varlistentry> - <term><emphasis role="bold">clientPort</emphasis></term> - - <listitem> - <para>the port to listen for client connections</para> - </listitem> - </varlistentry> - </variablelist> - - <para>Now that you created the configuration file, you can start - ZooKeeper:</para> - - <programlisting>bin/zkServer.sh start</programlisting> - - <para>ZooKeeper logs messages using log4j -- more detail - available in the - <ulink url="zookeeperProgrammers.html#Logging">Logging</ulink> - section of the Programmer's Guide. You will see log messages - coming to the console (default) and/or a log file depending on - the log4j configuration.</para> - - <para>The steps outlined here run ZooKeeper in standalone mode. There is - no replication, so if ZooKeeper process fails, the service will go down. - This is fine for most development situations, but to run ZooKeeper in - replicated mode, please see <ulink - url="#sc_RunningReplicatedZooKeeper">Running Replicated - ZooKeeper</ulink>.</para> - </section> - - <section id="sc_FileManagement"> - <title>Managing ZooKeeper Storage</title> - <para>For long running production systems ZooKeeper storage must - be managed externally (dataDir and logs). See the section on - <ulink - url="zookeeperAdmin.html#sc_maintenance">maintenance</ulink> for - more details.</para> - </section> - - <section id="sc_ConnectingToZooKeeper"> - <title>Connecting to ZooKeeper</title> - - <programlisting>$ bin/zkCli.sh -server 127.0.0.1:2181</programlisting> - - <para>This lets you perform simple, file-like operations.</para> - - <para>Once you have connected, you should see something like: - </para> - <programlisting> -<![CDATA[ -Connecting to localhost:2181 -log4j:WARN No appenders could be found for logger (org.apache.zookeeper.ZooKeeper). -log4j:WARN Please initialize the log4j system properly. -Welcome to ZooKeeper! -JLine support is enabled -[zkshell: 0] -]]> </programlisting> - <para> - From the shell, type <command>help</command> to get a listing of commands that can be executed from the client, as in: - </para> - <programlisting> -<![CDATA[ -[zkshell: 0] help -ZooKeeper host:port cmd args - get path [watch] - ls path [watch] - set path data [version] - delquota [-n|-b] path - quit - printwatches on|off - create path data acl - stat path [watch] - listquota path - history - setAcl path acl - getAcl path - sync path - redo cmdno - addauth scheme auth - delete path [version] - deleteall path - setquota -n|-b val path - -]]> </programlisting> - <para>From here, you can try a few simple commands to get a feel for this simple command line interface. First, start by issuing the list command, as - in <command>ls</command>, yielding: - </para> - <programlisting> -<![CDATA[ -[zkshell: 8] ls / -[zookeeper] -]]> </programlisting> - <para>Next, create a new znode by running <command>create /zk_test my_data</command>. This creates a new znode and associates the string "my_data" with the node. - You should see:</para> - <programlisting> -<![CDATA[ -[zkshell: 9] create /zk_test my_data -Created /zk_test -]]> </programlisting> - <para> Issue another <command>ls /</command> command to see what the directory looks like: - </para> - <programlisting> -<![CDATA[ -[zkshell: 11] ls / -[zookeeper, zk_test] - -]]> </programlisting><para> - Notice that the zk_test directory has now been created. - </para> - <para>Next, verify that the data was associated with the znode by running the <command>get</command> command, as in: - </para> - <programlisting> -<![CDATA[ -[zkshell: 12] get /zk_test -my_data -cZxid = 5 -ctime = Fri Jun 05 13:57:06 PDT 2009 -mZxid = 5 -mtime = Fri Jun 05 13:57:06 PDT 2009 -pZxid = 5 -cversion = 0 -dataVersion = 0 -aclVersion = 0 -ephemeralOwner = 0 -dataLength = 7 -numChildren = 0 -]]> </programlisting> - <para>We can change the data associated with zk_test by issuing the <command>set</command> command, as in: - </para> - <programlisting> -<![CDATA[ -[zkshell: 14] set /zk_test junk -cZxid = 5 -ctime = Fri Jun 05 13:57:06 PDT 2009 -mZxid = 6 -mtime = Fri Jun 05 14:01:52 PDT 2009 -pZxid = 5 -cversion = 0 -dataVersion = 1 -aclVersion = 0 -ephemeralOwner = 0 -dataLength = 4 -numChildren = 0 -[zkshell: 15] get /zk_test -junk -cZxid = 5 -ctime = Fri Jun 05 13:57:06 PDT 2009 -mZxid = 6 -mtime = Fri Jun 05 14:01:52 PDT 2009 -pZxid = 5 -cversion = 0 -dataVersion = 1 -aclVersion = 0 -ephemeralOwner = 0 -dataLength = 4 -numChildren = 0 -]]> </programlisting> - <para> - (Notice we did a <command>get</command> after setting the data and it did, indeed, change.</para> - <para>Finally, let's <command>delete</command> the node by issuing: - </para> - <programlisting> -<![CDATA[ -[zkshell: 16] delete /zk_test -[zkshell: 17] ls / -[zookeeper] -[zkshell: 18] -]]></programlisting> - <para>That's it for now. To explore more, continue with the rest of this document and see the <ulink url="zookeeperProgrammers.html">Programmer's Guide</ulink>. </para> - </section> - - <section id="sc_ProgrammingToZooKeeper"> - <title>Programming to ZooKeeper</title> - - <para>ZooKeeper has a Java bindings and C bindings. They are - functionally equivalent. The C bindings exist in two variants: single - threaded and multi-threaded. These differ only in how the messaging loop - is done. For more information, see the <ulink - url="zookeeperProgrammers.html#ch_programStructureWithExample">Programming - Examples in the ZooKeeper Programmer's Guide</ulink> for - sample code using of the different APIs.</para> - </section> - - <section id="sc_RunningReplicatedZooKeeper"> - <title>Running Replicated ZooKeeper</title> - - <para>Running ZooKeeper in standalone mode is convenient for evaluation, - some development, and testing. But in production, you should run - ZooKeeper in replicated mode. A replicated group of servers in the same - application is called a <emphasis>quorum</emphasis>, and in replicated - mode, all servers in the quorum have copies of the same configuration - file.</para> - <note> - <para> - For replicated mode, a minimum of three servers are required, - and it is strongly recommended that you have an odd number of - servers. If you only have two servers, then you are in a - situation where if one of them fails, there are not enough - machines to form a majority quorum. Two servers is inherently - <emphasis role="bold">less</emphasis> - stable than a single server, because there are two single - points of failure. - </para> - </note> - <para> - The required - <emphasis role="bold">conf/zoo.cfg</emphasis> - file for replicated mode is similar to the one used in standalone - mode, but with a few differences. Here is an example: - </para> - -<programlisting> -tickTime=2000 -dataDir=/var/lib/zookeeper -clientPort=2181 -initLimit=5 -syncLimit=2 -server.1=zoo1:2888:3888 -server.2=zoo2:2888:3888 -server.3=zoo3:2888:3888 -</programlisting> - - <para>The new entry, <emphasis role="bold">initLimit</emphasis> is - timeouts ZooKeeper uses to limit the length of time the ZooKeeper - servers in quorum have to connect to a leader. The entry <emphasis - role="bold">syncLimit</emphasis> limits how far out of date a server can - be from a leader.</para> - - <para>With both of these timeouts, you specify the unit of time using - <emphasis role="bold">tickTime</emphasis>. In this example, the timeout - for initLimit is 5 ticks at 2000 milleseconds a tick, or 10 - seconds.</para> - - <para>The entries of the form <emphasis>server.X</emphasis> list the - servers that make up the ZooKeeper service. When the server starts up, - it knows which server it is by looking for the file - <emphasis>myid</emphasis> in the data directory. That file has the - contains the server number, in ASCII.</para> - - <para>Finally, note the two port numbers after each server - name: " 2888" and "3888". Peers use the former port to connect - to other peers. Such a connection is necessary so that peers - can communicate, for example, to agree upon the order of - updates. More specifically, a ZooKeeper server uses this port - to connect followers to the leader. When a new leader arises, a - follower opens a TCP connection to the leader using this - port. Because the default leader election also uses TCP, we - currently require another port for leader election. This is the - second port in the server entry. - </para> - - <note> - <para>If you want to test multiple servers on a single - machine, specify the servername - as <emphasis>localhost</emphasis> with unique quorum & - leader election ports (i.e. 2888:3888, 2889:3889, 2890:3890 in - the example above) for each server.X in that server's config - file. Of course separate <emphasis>dataDir</emphasis>s and - distinct <emphasis>clientPort</emphasis>s are also necessary - (in the above replicated example, running on a - single <emphasis>localhost</emphasis>, you would still have - three config files).</para> - <para>Please be aware that setting up multiple servers on a single - machine will not create any redundancy. If something were to - happen which caused the machine to die, all of the zookeeper - servers would be offline. Full redundancy requires that each - server have its own machine. It must be a completely separate - physical server. Multiple virtual machines on the same physical - host are still vulnerable to the complete failure of that host.</para> - </note> - </section> - - <section> - <title>Other Optimizations</title> - - <para>There are a couple of other configuration parameters that can - greatly increase performance:</para> - - <itemizedlist> - <listitem> - <para>To get low latencies on updates it is important to - have a dedicated transaction log directory. By default - transaction logs are put in the same directory as the data - snapshots and <emphasis>myid</emphasis> file. The dataLogDir - parameters indicates a different directory to use for the - transaction logs.</para> - </listitem> - - <listitem> - <para><emphasis>[tbd: what is the other config param?]</emphasis></para> - </listitem> - </itemizedlist> - </section> - </section> -</article>
