Modified: helix/site-content/0.7.1-docs/tutorial_yaml.html URL: http://svn.apache.org/viewvc/helix/site-content/0.7.1-docs/tutorial_yaml.html?rev=1819859&r1=1819858&r2=1819859&view=diff ============================================================================== --- helix/site-content/0.7.1-docs/tutorial_yaml.html (original) +++ helix/site-content/0.7.1-docs/tutorial_yaml.html Tue Jan 2 17:32:45 2018 @@ -1,7 +1,7 @@ <!DOCTYPE html> <!-- - Generated by Apache Maven Doxia at 2017-10-14 + Generated by Apache Maven Doxia at 2018-01-02 Rendered using Maven Reflow Skin 1.0.0 (http://andriusvelykis.github.com/reflow-maven-skin) --> <html xml:lang="en" lang="en"> @@ -105,12 +105,14 @@ </div> <div> <ul class="breadcrumb"> + <li><a href="http://helix.incubator.apache.org/"; title="Apache Helix" class="externalLink">Apache Helix </a></li> + <li class="divider">/</li> <li><a href="../" title="Apache Helix">Apache Helix </a></li> <li class="divider">/</li> <li><a href="./" title="Release 0.7.1 (beta)">Release 0.7.1 (beta) </a></li> <li class="divider">/</li> <li> Tutorial - YAML Cluster Setup</li> - <li class="publishDate version-date pull-right">Last Published: 2017-10-14</li> + <li class="publishDate version-date pull-right">Last Published: 2018-01-02</li> </ul> </div> </header> @@ -287,7 +289,7 @@ YAMLClusterSetup.YAMLClusterConfig confi <div class="row"> <div class="span12"> <p class="pull-right"><a href="#">Back to top</a></p> - <p class="copyright">Copyright ©2017 <a href="https://www.apache.org/";>The Apache Software Foundation</a>. All Rights Reserved.</p> + <p class="copyright">Copyright ©2018 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. All Rights Reserved.</p> <p><a href="http://github.com/andriusvelykis/reflow-maven-skin"; title="Reflow Maven skin">Reflow Maven skin</a> by <a href="http://andrius.velykis.lt"; target="_blank" title="Andrius Velykis">Andrius Velykis</a>.</p> <div class="row span16">
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See the NOTICE file +distributed with this work for additional information +regarding copyright ownership. The ASF licenses this file +to you 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. --> +<p></p> +<div class="section"> + <div class="page-header"> + <h2 id="Features">Features</h2> + </div> + <div class="section"> + <h3 id="CONFIGURING_IDEALSTATE">CONFIGURING IDEALSTATE</h3> + <p>Read concepts page for definition of Idealstate.</p> + <p>The placement of partitions in a DDS is very critical for reliability and scalability of the system. For example, when a node fails, it is important that the partitions hosted on that node are reallocated evenly among the remaining nodes. Consistent hashing is one such algorithm that can guarantee this. Helix by default comes with a variant of consistent hashing based of the RUSH algorithm. </p> + <p>This means given a number of partitions, replicas and number of nodes Helix does the automatic assignment of partition to nodes such that</p> + <ul> + <li>Each node has the same number of partitions and replicas of the same partition do not stay on the same node.</li> + <li>When a node fails, the partitions will be equally distributed among the remaining nodes</li> + <li>When new nodes are added, the number of partitions moved will be minimized along with satisfying the above two criteria.</li> + </ul> + <p>Helix provides multiple ways to control the placement and state of a replica. </p> + <div class="source"> + <pre> |AUTO REBALANCE| AUTO | CUSTOM | + ----------------------------------------- + LOCATION | HELIX | APP | APP | + ----------------------------------------- + STATE | HELIX | HELIX | APP | + ----------------------------------------- +</pre> + </div> + <div class="section"> + <h4 id="HELIX_EXECUTION_MODE">HELIX EXECUTION MODE</h4> + <p>Idealstate is defined as the state of the DDS when all nodes are up and running and healthy. Helix uses this as the target state of the system and computes the appropriate transitions needed in the system to bring it to a stable state. </p> + <p>Helix supports 3 different execution modes which allows application to explicitly control the placement and state of the replica.</p> + <div class="section"> + <h5 id="AUTO_REBALANCE">AUTO_REBALANCE</h5> + <p>When the idealstate mode is set to AUTO_REBALANCE, Helix controls both the location of the replica along with the state. This option is useful for applications where creation of a replica is not expensive. Example</p> + <div class="source"> + <pre>{ + "id" : "MyResource", + "simpleFields" : { + "IDEAL_STATE_MODE" : "AUTO_REBALANCE", + "NUM_PARTITIONS" : "3", + "REPLICAS" : "2", + "STATE_MODEL_DEF_REF" : "MasterSlave", + } + "listFields" : { + "MyResource_0" : [], + "MyResource_1" : [], + "MyResource_2" : [] + }, + "mapFields" : { + } +} +</pre> + </div> + <p>If there are 3 nodes in the cluster, then Helix will internally compute the ideal state as </p> + <div class="source"> + <pre>{ + "id" : "MyResource", + "simpleFields" : { + "NUM_PARTITIONS" : "3", + "REPLICAS" : "2", + "STATE_MODEL_DEF_REF" : "MasterSlave", + }, + "mapFields" : { + "MyResource_0" : { + "N1" : "MASTER", + "N2" : "SLAVE", + }, + "MyResource_1" : { + "N2" : "MASTER", + "N3" : "SLAVE", + }, + "MyResource_2" : { + "N3" : "MASTER", + "N1" : "SLAVE", + } + } +} +</pre> + </div> + <p>Another typical example is evenly distributing a group of tasks among the currently alive processes. For example, if there are 60 tasks and 4 nodes, Helix assigns 15 tasks to each node. When one node fails Helix redistributes its 15 tasks to the remaining 3 nodes. Similarly, if a node is added, Helix re-allocates 3 tasks from each of the 4 nodes to the 5th node. </p> + </div> + </div> + <div class="section"> + <h4 id="AUTO">AUTO</h4> + <p>When the idealstate mode is set to AUTO, Helix only controls STATE of the replicas where as the location of the partition is controlled by application. Example: The below idealstate indicates thats âMyResource_0â must be only on node1 and node2. But gives the control of assigning the STATE to Helix.</p> + <div class="source"> + <pre>{ + "id" : "MyResource", + "simpleFields" : { + "IDEAL_STATE_MODE" : "AUTO", + "NUM_PARTITIONS" : "3", + "REPLICAS" : "2", + "STATE_MODEL_DEF_REF" : "MasterSlave", + } + "listFields" : { + "MyResource_0" : [node1, node2], + "MyResource_1" : [node2, node3], + "MyResource_2" : [node3, node1] + }, + "mapFields" : { + } +} +</pre> + </div> + <p>In this mode when node1 fails, unlike in AUTO-REBALANCE mode the partition is not moved from node1 to others nodes in the cluster. Instead, Helix will decide to change the state of MyResource_0 in N2 based on the system constraints. For example, if a system constraint specified that there should be 1 Master and if the Master failed, then node2 will be made the new master. </p> + </div> + <div class="section"> + <h4 id="CUSTOM">CUSTOM</h4> + <p>Helix offers a third mode called CUSTOM, in which application can completely control the placement and state of each replica. Applications will have to implement an interface that Helix will invoke when the cluster state changes. Within this callback, the application can recompute the idealstate. Helix will then issue appropriate transitions such that Idealstate and Currentstate converges.</p> + <div class="source"> + <pre>{ + "id" : "MyResource", + "simpleFields" : { + "IDEAL_STATE_MODE" : "CUSTOM", + "NUM_PARTITIONS" : "3", + "REPLICAS" : "2", + "STATE_MODEL_DEF_REF" : "MasterSlave", + }, + "mapFields" : { + "MyResource_0" : { + "N1" : "MASTER", + "N2" : "SLAVE", + }, + "MyResource_1" : { + "N2" : "MASTER", + "N3" : "SLAVE", + }, + "MyResource_2" : { + "N3" : "MASTER", + "N1" : "SLAVE", + } + } +} +</pre> + </div> + <p>For example, the current state of the system might be âMyResource_0â -> {N1:MASTER,N2:SLAVE} and the application changes the ideal state to âMyResource_0â -> {N1:SLAVE,N2:MASTER}. Helix will not blindly issue MASTERâ>SLAVE to N1 and SLAVEâ>MASTER to N2 in parallel since it might result in a transient state where both N1 and N2 are masters. Helix will first issue MASTERâ>SLAVE to N1 and after its completed it will issue SLAVEâ>MASTER to N2. </p> + </div> + </div> + <div class="section"> + <h3 id="State_Machine_Configuration">State Machine Configuration</h3> + <p>Helix comes with 3 default state models that are most commonly used. Its possible to have multiple state models in a cluster. Every resource that is added should have a reference to the state model. </p> + <ul> + <li>MASTER-SLAVE: Has 3 states OFFLINE,SLAVE,MASTER. Max masters is 1. Slaves will be based on the replication factor. Replication factor can be specified while adding the resource</li> + <li>ONLINE-OFFLINE: Has 2 states OFFLINE and ONLINE. Very simple state model and most applications start off with this state model.</li> + <li>LEADER-STANDBY:1 Leader and many stand bys. In general the standbyâs are idle.</li> + </ul> + <p>Apart from providing the state machine configuration, one can specify the constraints of states and transitions.</p> + <p>For example one can say Master:1. Max number of replicas in Master state at any time is 1. OFFLINE-SLAVE:5 Max number of Offline-Slave transitions that can happen concurrently in the system</p> + <p>STATE PRIORITY Helix uses greedy approach to satisfy the state constraints. For example if the state machine configuration says it needs 1 master and 2 slaves but only 1 node is active, Helix must promote it to master. This behavior is achieved by providing the state priority list as MASTER,SLAVE.</p> + <p>STATE TRANSITION PRIORITY Helix tries to fire as many transitions as possible in parallel to reach the stable state without violating constraints. By default Helix simply sorts the transitions alphabetically and fires as many as it can without violating the constraints. One can control this by overriding the priority order.</p> + </div> + <div class="section"> + <h3 id="Config_management">Config management</h3> + <p>Helix allows applications to store application specific properties. The configuration can have different scopes.</p> + <ul> + <li>Cluster</li> + <li>Node specific</li> + <li>Resource specific</li> + <li>Partition specific</li> + </ul> + <p>Helix also provides notifications when any configs are changed. This allows applications to support dynamic configuration changes.</p> + <p>See HelixManager.getConfigAccessor for more info</p> + </div> + <div class="section"> + <h3 id="Intra_cluster_messaging_api">Intra cluster messaging api</h3> + <p>This is an interesting feature which is quite useful in practice. Often times, nodes in DDS requires a mechanism to interact with each other. One such requirement is a process of bootstrapping a replica.</p> + <p>Consider a search system use case where the index replica starts up and it does not have an index. One of the commonly used solutions is to get the index from a common location or to copy the index from another replica. Helix provides a messaging api, that can be used to talk to other nodes in the system. The value added that Helix provides here is, message recipient can be specified in terms of resource, partition, state and Helix ensures that the message is delivered to all of the required recipients. In this particular use case, the instance can specify the recipient criteria as all replicas of P1. Since Helix is aware of the global state of the system, it can send the message to appropriate nodes. Once the nodes respond Helix provides the bootstrapping replica with all the responses.</p> + <p>This is a very generic api and can also be used to schedule various periodic tasks in the cluster like data backups etc. System Admins can also perform adhoc tasks like on demand backup or execute a system command(like rm -rf ;-)) across all nodes.</p> + <div class="source"> + <pre> ClusterMessagingService messagingService = manager.getMessagingService(); + //CONSTRUCT THE MESSAGE + Message requestBackupUriRequest = new Message( + MessageType.USER_DEFINE_MSG, UUID.randomUUID().toString()); + requestBackupUriRequest + .setMsgSubType(BootstrapProcess.REQUEST_BOOTSTRAP_URL); + requestBackupUriRequest.setMsgState(MessageState.NEW); + //SET THE RECIPIENT CRITERIA, All nodes that satisfy the criteria will receive the message + Criteria recipientCriteria = new Criteria(); + recipientCriteria.setInstanceName("%"); + recipientCriteria.setRecipientInstanceType(InstanceType.PARTICIPANT); + recipientCriteria.setResource("MyDB"); + recipientCriteria.setPartition(""); + //Should be processed only the process that is active at the time of sending the message. + //This means if the recipient is restarted after message is sent, it will not be processed. + recipientCriteria.setSessionSpecific(true); + // wait for 30 seconds + int timeout = 30000; + //The handler that will be invoked when any recipient responds to the message. + BootstrapReplyHandler responseHandler = new BootstrapReplyHandler(); + //This will return only after all recipients respond or after timeout. + int sentMessageCount = messagingService.sendAndWait(recipientCriteria, + requestBackupUriRequest, responseHandler, timeout); +</pre> + </div> + <p>See HelixManager.getMessagingService for more info.</p> + </div> + <div class="section"> + <h3 id="Application_specific_property_storage">Application specific property storage</h3> + <p>There are several usecases where applications needs support for distributed data structures. Helix uses Zookeeper to store the application data and hence provides notifications when the data changes. One value add Helix provides is the ability to specify cache the data and also write through cache. This is more efficient than reading from ZK every time.</p> + <p>See HelixManager.getHelixPropertyStore</p> + </div> + <div class="section"> + <h3 id="Throttling">Throttling</h3> + <p>Since all state changes in the system are triggered through transitions, Helix can control the number of transitions that can happen in parallel. Some of the transitions may be light weight but some might involve moving data around which is quite expensive. Helix allows applications to set threshold on transitions. The threshold can be set at the multiple scopes.</p> + <ul> + <li>MessageType e.g STATE_TRANSITION</li> + <li>TransitionType e.g SLAVE-MASTER</li> + <li>Resource e.g database</li> + <li>Node i.e per node max transitions in parallel.</li> + </ul> + <p>See HelixManager.getHelixAdmin.addMessageConstraint() </p> + </div> + <div class="section"> + <h3 id="Health_monitoring_and_alerting">Health monitoring and alerting</h3> + <p>This in currently in development mode, not yet productionized.</p> + <p>Helix provides ability for each node in the system to report health metrics on a periodic basis. Helix supports multiple ways to aggregate these metrics like simple SUM, AVG, EXPONENTIAL DECAY, WINDOW. Helix will only persist the aggregated value. Applications can define threshold on the aggregate values according to the SLAâs and when the SLA is violated Helix will fire an alert. Currently Helix only fires an alert but eventually we plan to use this metrics to either mark the node dead or load balance the partitions. This feature will be valuable in for distributed systems that support multi-tenancy and have huge variation in work load patterns. Another place this can be used is to detect skewed partitions and rebalance the cluster.</p> + <p>This feature is not yet stable and do not recommend to be used in production.</p> + </div> + <div class="section"> + <h3 id="Controller_deployment_modes">Controller deployment modes</h3> + <p>Read Architecture wiki for more details on the Role of a controller. In simple words, it basically controls the participants in the cluster by issuing transitions.</p> + <p>Helix provides multiple options to deploy the controller.</p> + <div class="section"> + <h4 id="STANDALONE">STANDALONE</h4> + <p>Controller can be started as a separate process to manage a cluster. This is the recommended approach. How ever since one controller can be a single point of failure, multiple controller processes are required for reliability. Even if multiple controllers are running only one will be actively managing the cluster at any time and is decided by a leader election process. If the leader fails, another leader will resume managing the cluster.</p> + <p>Even though we recommend this method of deployment, it has the drawback of having to manage an additional service for each cluster. See Controller As a Service option.</p> + </div> + <div class="section"> + <h4 id="EMBEDDED">EMBEDDED</h4> + <p>If setting up a separate controller process is not viable, then it is possible to embed the controller as a library in each of the participant. </p> + </div> + <div class="section"> + <h4 id="CONTROLLER_AS_A_SERVICE">CONTROLLER AS A SERVICE</h4> + <p>One of the cool feature we added in helix was use a set of controllers to manage a large number of clusters. For example if you have X clusters to be managed, instead of deploying X*3(3 controllers for fault tolerance) controllers for each cluster, one can deploy only 3 controllers. Each controller can manage X/3 clusters. If any controller fails the remaining two will manage X/2 clusters. 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See the NOTICE file +distributed with this work for additional information +regarding copyright ownership. The ASF licenses this file +to you 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. --> +<p></p> +<div class="section"> + <div class="page-header"> + <h2 id="Quickstart">Quickstart</h2> + </div> +</div> +<div class="section"> + <h2 id="Get_Helix">Get Helix</h2> + <p>First, let's get Helix. Either build it, or download it.</p> + <div class="section"> + <h3 id="Build">Build</h3> + <div class="source"> + <pre>git clone https://git-wip-us.apache.org/repos/asf/helix.git +cd helix +git checkout tags/helix-0.8.0 +mvn install package -DskipTests +cd helix-core/target/helix-core-pkg/bin # This folder contains all the scripts used in following sections +chmod +x * +</pre> + </div> + </div> + <div class="section"> + <h3 id="Download">Download</h3> + <p>Download the 0.8.0 release package <a href="./download.html">here</a></p> + </div> +</div> +<div class="section"> + <h2 id="Overview">Overview</h2> + <p>In this Quickstart, we'll set up a master-slave replicated, partitioned system. Then we'll demonstrate how to add a node, rebalance the partitions, and show how Helix manages failover.</p> +</div> +<div class="section"> + <h2 id="Lets_Do_It">Let's Do It</h2> + <p>Helix provides command line interfaces to set up the cluster and view the cluster state. The best way to understand how Helix views a cluster is to build a cluster.</p> + <div class="section"> + <h3 id="Get_to_the_Tools_Directory">Get to the Tools Directory</h3> + <p>If you built the code:</p> + <div class="source"> + <pre>cd helix/helix/helix-core/target/helix-core-pkg/bin +</pre> + </div> + <p>If you downloaded the release package, extract it.</p> + </div> +</div> +<div class="section"> + <h2 id="Short_Version">Short Version</h2> + <p>You can observe the components working together in this demo, which does the following:</p> + <ul> + <li>Create a cluster</li> + <li>Add 2 nodes (participants) to the cluster</li> + <li>Set up a resource with 6 partitions and 2 replicas: 1 Master, and 1 Slave per partition</li> + <li>Show the cluster state after Helix balances the partitions</li> + <li>Add a third node</li> + <li>Show the cluster state. Note that the third node has taken mastership of 2 partitions.</li> + <li>Kill the third node (Helix takes care of failover)</li> + <li>Show the cluster state. Note that the two surviving nodes take over mastership of the partitions from the failed node</li> + </ul> + <div class="section"> + <h3 id="Run_the_Demo">Run the Demo</h3> + <div class="source"> + <pre>cd helix/helix/helix-core/target/helix-core-pkg/bin +./quickstart.sh +</pre> + </div> + <div class="section"> + <h4 id="The_Initial_Setup">The Initial Setup</h4> + <p>2 nodes are set up and the partitions are rebalanced.</p> + <p>The cluster state is as follows:</p> + <div class="source"> + <pre>CLUSTER STATE: After starting 2 nodes + localhost_12000 localhost_12001 +MyResource_0 M S +MyResource_1 S M +MyResource_2 M S +MyResource_3 M S +MyResource_4 S M +MyResource_5 S M +</pre> + </div> + <p>Note there is one master and one slave per partition.</p> + </div> + <div class="section"> + <h4 id="Add_a_Node">Add a Node</h4> + <p>A third node is added and the cluster is rebalanced.</p> + <p>The cluster state changes to:</p> + <div class="source"> + <pre>CLUSTER STATE: After adding a third node + localhost_12000 localhost_12001 localhost_12002 +MyResource_0 S M S +MyResource_1 S S M +MyResource_2 M S S +MyResource_3 S S M +MyResource_4 M S S +MyResource_5 S M S +</pre> + </div> + <p>Note there is one master and <i>two</i> slaves per partition. This is expected because there are three nodes.</p> + </div> + <div class="section"> + <h4 id="Kill_a_Node">Kill a Node</h4> + <p>Finally, a node is killed to simulate a failure</p> + <p>Helix makes sure each partition has a master. The cluster state changes to:</p> + <div class="source"> + <pre>CLUSTER STATE: After the 3rd node stops/crashes + localhost_12000 localhost_12001 localhost_12002 +MyResource_0 S M - +MyResource_1 S M - +MyResource_2 M S - +MyResource_3 M S - +MyResource_4 M S - +MyResource_5 S M - +</pre> + </div> + </div> + </div> +</div> +<div class="section"> + <h2 id="Long_Version">Long Version</h2> + <p>Now you can run the same steps by hand. In this detailed version, we'll do the following:</p> + <ul> + <li>Define a cluster</li> + <li>Add two nodes to the cluster</li> + <li>Add a 6-partition resource with 1 master and 2 slave replicas per partition</li> + <li>Verify that the cluster is healthy and inspect the Helix view</li> + <li>Expand the cluster: add a few nodes and rebalance the partitions</li> + <li>Failover: stop a node and verify the mastership transfer</li> + </ul> + <div class="section"> + <h3 id="Install_and_Start_ZooKeeper">Install and Start ZooKeeper</h3> + <p>Zookeeper can be started in standalone mode or replicated mode.</p> + <p>More information is available at</p> + <ul> + <li><a class="externalLink" href="http://zookeeper.apache.org/doc/r3.3.3/zookeeperStarted.html";>http://zookeeper.apache.org/doc/r3.3.3/zookeeperStarted.html</a></li> + <li><a class="externalLink" href="http://zookeeper.apache.org/doc/trunk/zookeeperAdmin.html#sc_zkMulitServerSetup";>http://zookeeper.apache.org/doc/trunk/zookeeperAdmin.html#sc_zkMulitServerSetup</a></li> + </ul> + <p>In this example, let's start zookeeper in local mode.</p> + <div class="section"> + <h4 id="Start_ZooKeeper_Locally_on_Port_2199">Start ZooKeeper Locally on Port 2199</h4> + <div class="source"> + <pre>./start-standalone-zookeeper.sh 2199 & +</pre> + </div> + </div> + </div> + <div class="section"> + <h3 id="Define_the_Cluster">Define the Cluster</h3> + <p>The helix-admin tool is used for cluster administration tasks. In the Quickstart, we'll use the command line interface. Helix supports a REST interface as well.</p> + <p>zookeeper_address is of the format host:port e.g localhost:2199 for standalone or host1:port,host2:port for multi-node.</p> + <p>Next, we'll set up a cluster MYCLUSTER cluster with these attributes:</p> + <ul> + <li>3 instances running on localhost at ports 12913,12914,12915</li> + <li>One database named myDB with 6 partitions</li> + <li>Each partition will have 3 replicas with 1 master, 2 slaves</li> + <li>ZooKeeper running locally at localhost:2199</li> + </ul> + <div class="section"> + <h4 id="Create_the_Cluster_MYCLUSTER">Create the Cluster MYCLUSTER</h4> + <div class="source"> + <pre># ./helix-admin.sh --zkSvr <zk_address> --addCluster <clustername> +./helix-admin.sh --zkSvr localhost:2199 --addCluster MYCLUSTER +</pre> + </div> + </div> + </div> + <div class="section"> + <h3 id="Add_Nodes_to_the_Cluster">Add Nodes to the Cluster</h3> + <p>In this case we'll add three nodes: localhost:12913, localhost:12914, localhost:12915</p> + <div class="source"> + <pre># helix-admin.sh --zkSvr <zk_address> --addNode <clustername> <host:port> +./helix-admin.sh --zkSvr localhost:2199 --addNode MYCLUSTER localhost:12913 +./helix-admin.sh --zkSvr localhost:2199 --addNode MYCLUSTER localhost:12914 +./helix-admin.sh --zkSvr localhost:2199 --addNode MYCLUSTER localhost:12915 +</pre> + </div> + </div> + <div class="section"> + <h3 id="Define_the_Resource_and_Partitioning">Define the Resource and Partitioning</h3> + <p>In this example, the resource is a database, partitioned 6 ways. Note that in a production system, it's common to over-partition for better load balancing. Helix has been used in production to manage hundreds of databases each with 10s or 100s of partitions running on 10s of physical nodes.</p> + <div class="section"> + <h4 id="Create_a_Database_with_6_Partitions_using_the_MasterSlave_State_Model">Create a Database with 6 Partitions using the MasterSlave State Model</h4> + <p>Helix ensures there will be exactly one master for each partition.</p> + <div class="source"> + <pre># helix-admin.sh --zkSvr <zk_address> --addResource <clustername> <resourceName> <numPartitions> <StateModelName> +./helix-admin.sh --zkSvr localhost:2199 --addResource MYCLUSTER myDB 6 MasterSlave +</pre> + </div> + </div> + <div class="section"> + <h4 id="Let_Helix_Assign_Partitions_to_Nodes">Let Helix Assign Partitions to Nodes</h4> + <p>This command will distribute the partitions amongst all the nodes in the cluster. In this example, each partition has 3 replicas.</p> + <div class="source"> + <pre># helix-admin.sh --zkSvr <zk_address> --rebalance <clustername> <resourceName> <replication factor> +./helix-admin.sh --zkSvr localhost:2199 --rebalance MYCLUSTER myDB 3 +</pre> + </div> + <p>Now the cluster is defined in ZooKeeper. The nodes (localhost:12913, localhost:12914, localhost:12915) and resource (myDB, with 6 partitions using the MasterSlave model) are all properly configured. And the <i>IdealState</i> has been calculated, assuming a replication factor of 3.</p> + </div> + </div> + <div class="section"> + <h3 id="Start_the_Helix_Controller">Start the Helix Controller</h3> + <p>Now that the cluster is defined in ZooKeeper, the Helix controller can manage the cluster.</p> + <div class="source"> + <pre># Start the cluster manager, which will manage MYCLUSTER +./run-helix-controller.sh --zkSvr localhost:2199 --cluster MYCLUSTER 2>&1 > /tmp/controller.log & +</pre> + </div> + </div> + <div class="section"> + <h3 id="Start_up_the_Cluster_to_be_Managed">Start up the Cluster to be Managed</h3> + <p>We've started up ZooKeeper, defined the cluster, the resources, the partitioning, and started up the Helix controller. Next, we'll start up the nodes of the system to be managed. Each node is a Participant, which is an instance of the system component to be managed. Helix assigns work to Participants, keeps track of their roles and health, and takes action when a node fails.</p> + <div class="source"> + <pre># start up each instance. These are mock implementations that are actively managed by Helix +./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12913 --stateModelType MasterSlave 2>&1 > /tmp/participant_12913.log +./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12914 --stateModelType MasterSlave 2>&1 > /tmp/participant_12914.log +./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12915 --stateModelType MasterSlave 2>&1 > /tmp/participant_12915.log +</pre> + </div> + </div> + <div class="section"> + <h3 id="Inspect_the_Cluster">Inspect the Cluster</h3> + <p>Now, let's see the Helix view of our cluster. We'll work our way down as follows:</p> + <div class="source"> + <pre>Clusters -> MYCLUSTER -> instances -> instance detail + -> resources -> resource detail + -> partitions +</pre> + </div> + <p>A single Helix controller can manage multiple clusters, though so far, we've only defined one cluster. Let's see:</p> + <div class="source"> + <pre># List existing clusters +./helix-admin.sh --zkSvr localhost:2199 --listClusters + +Existing clusters: +MYCLUSTER +</pre> + </div> + <p>Now, let's see the Helix view of MYCLUSTER:</p> + <div class="source"> + <pre># helix-admin.sh --zkSvr <zk_address> --listClusterInfo <clusterName> +./helix-admin.sh --zkSvr localhost:2199 --listClusterInfo MYCLUSTER + +Existing resources in cluster MYCLUSTER: +myDB +Instances in cluster MYCLUSTER: +localhost_12915 +localhost_12914 +localhost_12913 +</pre> + </div> + <p>Let's look at the details of an instance:</p> + <div class="source"> + <pre># ./helix-admin.sh --zkSvr <zk_address> --listInstanceInfo <clusterName> <InstanceName> +./helix-admin.sh --zkSvr localhost:2199 --listInstanceInfo MYCLUSTER localhost_12913 + +InstanceConfig: { + "id" : "localhost_12913", + "mapFields" : { + }, + "listFields" : { + }, + "simpleFields" : { + "HELIX_ENABLED" : "true", + "HELIX_HOST" : "localhost", + "HELIX_PORT" : "12913" + } +} +</pre> + </div> + <div class="section"> + <h4 id="Query_Information_about_a_Resource">Query Information about a Resource</h4> + <div class="source"> + <pre># helix-admin.sh --zkSvr <zk_address> --listResourceInfo <clusterName> <resourceName> +./helix-admin.sh --zkSvr localhost:2199 --listResourceInfo MYCLUSTER myDB + +IdealState for myDB: +{ + "id" : "myDB", + "mapFields" : { + "myDB_0" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "MASTER", + "localhost_12915" : "SLAVE" + }, + "myDB_1" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "SLAVE", + "localhost_12915" : "MASTER" + }, + "myDB_2" : { + "localhost_12913" : "MASTER", + "localhost_12914" : "SLAVE", + "localhost_12915" : "SLAVE" + }, + "myDB_3" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "SLAVE", + "localhost_12915" : "MASTER" + }, + "myDB_4" : { + "localhost_12913" : "MASTER", + "localhost_12914" : "SLAVE", + "localhost_12915" : "SLAVE" + }, + "myDB_5" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "MASTER", + "localhost_12915" : "SLAVE" + } + }, + "listFields" : { + "myDB_0" : [ "localhost_12914", "localhost_12913", "localhost_12915" ], + "myDB_1" : [ "localhost_12915", "localhost_12913", "localhost_12914" ], + "myDB_2" : [ "localhost_12913", "localhost_12915", "localhost_12914" ], + "myDB_3" : [ "localhost_12915", "localhost_12913", "localhost_12914" ], + "myDB_4" : [ "localhost_12913", "localhost_12914", "localhost_12915" ], + "myDB_5" : [ "localhost_12914", "localhost_12915", "localhost_12913" ] + }, + "simpleFields" : { + "IDEAL_STATE_MODE" : "AUTO", + "REBALANCE_MODE" : "SEMI_AUTO", + "NUM_PARTITIONS" : "6", + "REPLICAS" : "3", + "STATE_MODEL_DEF_REF" : "MasterSlave", + "STATE_MODEL_FACTORY_NAME" : "DEFAULT" + } +} + +ExternalView for myDB: +{ + "id" : "myDB", + "mapFields" : { + "myDB_0" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "MASTER", + "localhost_12915" : "SLAVE" + }, + "myDB_1" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "SLAVE", + "localhost_12915" : "MASTER" + }, + "myDB_2" : { + "localhost_12913" : "MASTER", + "localhost_12914" : "SLAVE", + "localhost_12915" : "SLAVE" + }, + "myDB_3" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "SLAVE", + "localhost_12915" : "MASTER" + }, + "myDB_4" : { + "localhost_12913" : "MASTER", + "localhost_12914" : "SLAVE", + "localhost_12915" : "SLAVE" + }, + "myDB_5" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "MASTER", + "localhost_12915" : "SLAVE" + } + }, + "listFields" : { + }, + "simpleFields" : { + "BUCKET_SIZE" : "0" + } +} +</pre> + </div> + <p>Now, let's look at one of the partitions:</p> + <div class="source"> + <pre># helix-admin.sh --zkSvr <zk_address> --listResourceInfo <clusterName> <partition> +./helix-admin.sh --zkSvr localhost:2199 --listResourceInfo mycluster myDB_0 +</pre> + </div> + </div> + </div> + <div class="section"> + <h3 id="Expand_the_Cluster">Expand the Cluster</h3> + <p>Next, we'll show how Helix does the work that you'd otherwise have to build into your system. When you add capacity to your cluster, you want the work to be evenly distributed. In this example, we started with 3 nodes, with 6 partitions. The partitions were evenly balanced, 2 masters and 4 slaves per node. Let's add 3 more nodes: localhost:12916, localhost:12917, localhost:12918</p> + <div class="source"> + <pre>./helix-admin.sh --zkSvr localhost:2199 --addNode MYCLUSTER localhost:12916 +./helix-admin.sh --zkSvr localhost:2199 --addNode MYCLUSTER localhost:12917 +./helix-admin.sh --zkSvr localhost:2199 --addNode MYCLUSTER localhost:12918 +</pre> + </div> + <p>And start up these instances:</p> + <div class="source"> + <pre># start up each instance. These are mock implementations that are actively managed by Helix +./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12916 --stateModelType MasterSlave 2>&1 > /tmp/participant_12916.log +./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12917 --stateModelType MasterSlave 2>&1 > /tmp/participant_12917.log +./start-helix-participant.sh --zkSvr localhost:2199 --cluster MYCLUSTER --host localhost --port 12918 --stateModelType MasterSlave 2>&1 > /tmp/participant_12918.log +</pre> + </div> + <p>And now, let Helix do the work for you. To shift the work, simply rebalance. After the rebalance, each node will have one master and two slaves.</p> + <div class="source"> + <pre>./helix-admin.sh --zkSvr localhost:2199 --rebalance MYCLUSTER myDB 3 +</pre> + </div> + </div> + <div class="section"> + <h3 id="View_the_Cluster">View the Cluster</h3> + <p>OK, let's see how it looks:</p> + <div class="source"> + <pre>./helix-admin.sh --zkSvr localhost:2199 --listResourceInfo MYCLUSTER myDB + +IdealState for myDB: +{ + "id" : "myDB", + "mapFields" : { + "myDB_0" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "SLAVE", + "localhost_12917" : "MASTER" + }, + "myDB_1" : { + "localhost_12916" : "SLAVE", + "localhost_12917" : "SLAVE", + "localhost_12918" : "MASTER" + }, + "myDB_2" : { + "localhost_12913" : "MASTER", + "localhost_12917" : "SLAVE", + "localhost_12918" : "SLAVE" + }, + "myDB_3" : { + "localhost_12915" : "MASTER", + "localhost_12917" : "SLAVE", + "localhost_12918" : "SLAVE" + }, + "myDB_4" : { + "localhost_12916" : "MASTER", + "localhost_12917" : "SLAVE", + "localhost_12918" : "SLAVE" + }, + "myDB_5" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "MASTER", + "localhost_12915" : "SLAVE" + } + }, + "listFields" : { + "myDB_0" : [ "localhost_12917", "localhost_12913", "localhost_12914" ], + "myDB_1" : [ "localhost_12918", "localhost_12917", "localhost_12916" ], + "myDB_2" : [ "localhost_12913", "localhost_12917", "localhost_12918" ], + "myDB_3" : [ "localhost_12915", "localhost_12917", "localhost_12918" ], + "myDB_4" : [ "localhost_12916", "localhost_12917", "localhost_12918" ], + "myDB_5" : [ "localhost_12914", "localhost_12915", "localhost_12913" ] + }, + "simpleFields" : { + "IDEAL_STATE_MODE" : "AUTO", + "REBALANCE_MODE" : "SEMI_AUTO", + "NUM_PARTITIONS" : "6", + "REPLICAS" : "3", + "STATE_MODEL_DEF_REF" : "MasterSlave", + "STATE_MODEL_FACTORY_NAME" : "DEFAULT" + } +} + +ExternalView for myDB: +{ + "id" : "myDB", + "mapFields" : { + "myDB_0" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "SLAVE", + "localhost_12917" : "MASTER" + }, + "myDB_1" : { + "localhost_12916" : "SLAVE", + "localhost_12917" : "SLAVE", + "localhost_12918" : "MASTER" + }, + "myDB_2" : { + "localhost_12913" : "MASTER", + "localhost_12917" : "SLAVE", + "localhost_12918" : "SLAVE" + }, + "myDB_3" : { + "localhost_12915" : "MASTER", + "localhost_12917" : "SLAVE", + "localhost_12918" : "SLAVE" + }, + "myDB_4" : { + "localhost_12916" : "MASTER", + "localhost_12917" : "SLAVE", + "localhost_12918" : "SLAVE" + }, + "myDB_5" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "MASTER", + "localhost_12915" : "SLAVE" + } + }, + "listFields" : { + }, + "simpleFields" : { + "BUCKET_SIZE" : "0" + } +} +</pre> + </div> + <p>Mission accomplished. The partitions are nicely balanced.</p> + </div> + <div class="section"> + <h3 id="How_about_Failover">How about Failover?</h3> + <p>Building a fault tolerant system isn't trivial, but with Helix, it's easy. Helix detects a failed instance, and triggers mastership transfer automatically.</p> + <p>First, letâs fail an instance. In this example, we'll kill localhost:12918 to simulate a failure.</p> + <p>We lost localhost:12918, so myDB_1 lost its MASTER. Helix can fix that, it will transfer mastership to a healthy node that is currently a SLAVE, say localhost:12197. Helix balances the load as best as it can, given there are 6 partitions on 5 nodes. Let's see:</p> + <div class="source"> + <pre>./helix-admin.sh --zkSvr localhost:2199 --listResourceInfo MYCLUSTER myDB + +IdealState for myDB: +{ + "id" : "myDB", + "mapFields" : { + "myDB_0" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "SLAVE", + "localhost_12917" : "MASTER" + }, + "myDB_1" : { + "localhost_12916" : "SLAVE", + "localhost_12917" : "SLAVE", + "localhost_12918" : "MASTER" + }, + "myDB_2" : { + "localhost_12913" : "MASTER", + "localhost_12917" : "SLAVE", + "localhost_12918" : "SLAVE" + }, + "myDB_3" : { + "localhost_12915" : "MASTER", + "localhost_12917" : "SLAVE", + "localhost_12918" : "SLAVE" + }, + "myDB_4" : { + "localhost_12916" : "MASTER", + "localhost_12917" : "SLAVE", + "localhost_12918" : "SLAVE" + }, + "myDB_5" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "MASTER", + "localhost_12915" : "SLAVE" + } + }, + "listFields" : { + "myDB_0" : [ "localhost_12917", "localhost_12913", "localhost_12914" ], + "myDB_1" : [ "localhost_12918", "localhost_12917", "localhost_12916" ], + "myDB_2" : [ "localhost_12913", "localhost_12918", "localhost_12917" ], + "myDB_3" : [ "localhost_12915", "localhost_12918", "localhost_12917" ], + "myDB_4" : [ "localhost_12916", "localhost_12917", "localhost_12918" ], + "myDB_5" : [ "localhost_12914", "localhost_12915", "localhost_12913" ] + }, + "simpleFields" : { + "IDEAL_STATE_MODE" : "AUTO", + "REBALANCE_MODE" : "SEMI_AUTO", + "NUM_PARTITIONS" : "6", + "REPLICAS" : "3", + "STATE_MODEL_DEF_REF" : "MasterSlave", + "STATE_MODEL_FACTORY_NAME" : "DEFAULT" + } +} + +ExternalView for myDB: +{ + "id" : "myDB", + "mapFields" : { + "myDB_0" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "SLAVE", + "localhost_12917" : "MASTER" + }, + "myDB_1" : { + "localhost_12916" : "SLAVE", + "localhost_12917" : "MASTER" + }, + "myDB_2" : { + "localhost_12913" : "MASTER", + "localhost_12917" : "SLAVE" + }, + "myDB_3" : { + "localhost_12915" : "MASTER", + "localhost_12917" : "SLAVE" + }, + "myDB_4" : { + "localhost_12916" : "MASTER", + "localhost_12917" : "SLAVE" + }, + "myDB_5" : { + "localhost_12913" : "SLAVE", + "localhost_12914" : "MASTER", + "localhost_12915" : "SLAVE" + } + }, + "listFields" : { + }, + "simpleFields" : { + "BUCKET_SIZE" : "0" + } +} +</pre> + </div> + <p>As we've seen in this Quickstart, Helix takes care of partitioning, load balancing, elasticity, failure detection and recovery.</p> + </div> + <div class="section"> + <h3 id="ZooInspector">ZooInspector</h3> + <p>You can view all of the underlying data by going direct to zookeeper. Use ZooInspector that comes with zookeeper to browse the data. This is a java applet (make sure you have X windows)</p> + <p>To start zooinspector run the following command from <zk_install_directory>/contrib/ZooInspector</p> + <div class="source"> + <pre>java -cp zookeeper-3.3.3-ZooInspector.jar:lib/jtoaster-1.0.4.jar:../../lib/log4j-1.2.15.jar:../../zookeeper-3.3.3.jar org.apache.zookeeper.inspector.ZooInspector +</pre> + </div> + </div> + <div class="section"> + <h3 id="Next">Next</h3> + <p>Now that you understand the idea of Helix, read the <a href="./Tutorial.html">tutorial</a> to learn how to choose the right state model and constraints for your system, and how to implement it. In many cases, the built-in features meet your requirements. And best of all, Helix is a customizable framework, so you can plug in your own behavior, while retaining the automation provided by Helix.</p> + </div> +</div> + </div> + </div> + </div> + </div> + + </div><!-- /container --> + + <!-- Footer + ================================================== --> + <footer class="well"> + <div class="container"> + <div class="row"> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Get Helix</li> + <li> + <a href="download.html" title="Download">Download </a> + </li> + <li> + <a href="Building.html" title="Building">Building </a> + </li> + <li> + <a href="releasenotes/release-0.8.0.html" title="Release Notes">Release Notes </a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Hands-On</li> + <li class="active"> + <a href="#" title="Quick Start">Quick Start </a> + </li> + <li> + <a href="Tutorial.html" title="Tutorial">Tutorial </a> + </li> + <li> + <a href="../javadocs/0.8.0" title="Javadocs">Javadocs </a> + </li> + </ul> + </div> + <div class="span3 bottom-nav"> + <ul class="nav nav-list"> + <li class="nav-header">Recipes</li> + <li> + <a href="recipes/lock_manager.html" title="Distributed lock manager">Distributed lock manager </a> + </li> + <li> + <a href="recipes/rabbitmq_consumer_group.html" title="Rabbit MQ consumer group">Rabbit MQ consumer group </a> + </li> + <li> + <a href="recipes/rsync_replicated_file_store.html" title="Rsync replicated file store">Rsync replicated file store </a> + </li> + <li> + <a href="recipes/service_discovery.html" title="Service discovery">Service discovery </a> + </li> + <li> + <a href="recipes/task_dag_execution.html" title="Distributed task DAG execution">Distributed task DAG execution </a> + </li> + </ul> + </div> + </div> + </div> + </footer> + + <div class="container subfooter"> + <div class="row"> + <div class="span12"> + <p class="pull-right"><a href="#">Back to top</a></p> + <p class="copyright">Copyright ©2018 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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