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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="Helix_Tutorial:_Cloud_Support"><a href="./Tutorial.html">Helix Tutorial</a>: Cloud Support</h2> + </div> + <p>There are emerging cases to use Helix in a cloud environment, especially in those well-known public cloud, e.g. Azure, AWS, GCP, etc. Compared to previous on premise use cases, Helix has faced both challenges and opportunities in providing cloud related support. </p> + <p>As a first step, Helix implemented the support for participant auto registration in a cloud environment, which leverages the common feature of public cloud and facilitates Helix users when they need to create a cluster and register the participants to the cluster.</p> + <p>After a Helix cluster is created, there are two ways to add instances (or participants, we will use them interchangeably in this tutorial) to the cluster. One is manual add, where users call their own scripts to add instance config to the cluster for each participant; and the other is auto join, where users set the auto join config of the cluster to be true, and each participant populates its own hostname, port number, and other information in instance config during connection. However, in an on premise environment, the auto join only works perfectly when users use Helix in a non rack-aware environment, meaning there is no fault domain concept. For a rack-aware environment, users still need to manually input the domain information to the instance config as it is hard for each participant to get its own fault domain information. Considering most users would use Helix in a rack-aware environment, it means manual work is still required.</p> + <p>In a cloud environment, there is a good opportunity to achieve full automation as public cloud providers give domain information to each individual instance through a metadata endpoint. All of the above mentioned public cloud providers use a unique non-routable IP address (169.254.169.254) for this purpose. It can be accessed only from within the instance to retrieve the instance metadata information, which you can use to configure or manage the running instance. </p> + <p>More specifically, in AWS, Azure, and GCP, the query to the fixed IP address <a class="externalLink" href="http://169.254.169.254/";>http://169.254.169.254/</a> inside each instance will return its metadata information that contains domain information. In AWS, the field is named as âplacementâ; in Azure, the field is named as âPlatformUpdateDomainâ; and in GCP, the field is named as âzoneâ. It is usually just an integer denoting which fault domain the instance belongs to. This particular feature of public cloud is leveraged by Helix in cluster creation and partition registration process. </p> + <div class="section"> + <h3 id="What_Helix_Provides_for_Cloud_Environment">What Helix Provides for Cloud Environment</h3> + <ul> + <li>Provide definition of Helix cloud configs at cluster level and participant level</li> + <li>Provide enhanced REST and Java APIs for cluster creation and cloud config update</li> + <li>Provide generic interface for fetching and parsing cloud instance information</li> + <li>Provide the implementation of Azure cloud instance information processor</li> + <li>Provide the implementation of participant auto registration logic</li> + </ul> + </div> + <div class="section"> + <h3 id="How_to_Use_Cloud_Support">How to Use Cloud Support</h3> + <p>First of all, you need to make sure that your environment is indeed a cloud environment. Otherwise, all the assumptions in this support will not hold. Then depending on what kind of cloud environment you are in, you will need to perform some or all of the following steps.</p> + <div class="section"> + <h4 id="Define_Cloud_config_at_Cluster_Level">Define Cloud config at Cluster Level</h4> + <p>Helix provides cloud configs at two different levels, one is at cluster level, and the other is at participant level. We describe them separately.</p> + <p>At cluster level, we have a new Znode called CloudConfig. It has a few fields that store the relatively static cloud information for the whole cluster. Similar to other existing configs, Helix provides cloud config builder, validation, get/set functions. As the following table shows, the first two fields are required, and the last three fields are optional. </p> + <p><tt>CLOUD_ENABLED</tt> must be set to true if the user would like to use Helix cloud support. <tt>CLOUD_PROVIDER</tt> is the type of the cloud environment. Besides the few well-known public cloud providers, the user can also define his/her cloud environment as âCUSTOMIZEDâ. <tt>CLOUD_ID</tt> is an optional field. It can be used to record any specific metadata information the user would like to record, e.g. the ID for the particular cluster inside a cloud environment, etc. If the user chooses to use the provider that already has default implementations in Helix, e.g., Azure, he does not need to provide the last two fields, as Helix already provides the default value for these two fields in system property, which is considered as a bundle with Azure implementation that would be discussed later. If the user uses customized providers, or chooses some other cloud environment that has not been implemented in Helix yet, the user needs to provide the last two fields and/or < tt>CLOUD_ID</tt> depending on his/her usage. </p> + <table border="0" class="bodyTable table table-striped table-hover"> + <thead> + <tr class="a"> + <th>Field </th> + <th>Meaning </th> + </tr> + </thead> + <tbody> + <tr class="b"> + <td>CLOUD_ENABLED </td> + <td>determine whether the cluster is inside cloud environment and use Helix cloud support </td> + </tr> + <tr class="a"> + <td>CLOUD_PROVIDER </td> + <td>denote what kind of cloud environment the cluster is in, e.g. Azure, AWS, GCP, or CUSTOMIZED </td> + </tr> + <tr class="b"> + <td>CLOUD_ID </td> + <td>the specific id in cloud environment that belongs to this cluster </td> + </tr> + <tr class="a"> + <td>CLOUD_INFO_SOURCE </td> + <td>the source for retrieving the cloud information. </td> + </tr> + <tr class="b"> + <td>CLOUD_INFO_PROCESSOR_NAME </td> + <td>the name of the function that processes the fetching and parsing of cloud information </td> + </tr> + </tbody> + </table> + <p>Users could use either REST API or Java API to set these configs.</p> + <div class="section"> + <h5 id="REST_API_Examples">REST API Examples</h5> + <p>Helix enhanced current cluster creation REST API as well as Java API with extra fields that represent cloud related input. For example, in the following modified <tt>createCluster</tt> API, <tt>addCloudConfig</tt> is a Boolean value denotes whether to create with cloud config, and the <tt>cloudConfigManifest</tt> is the cloud config string, which will be converted to a Znode record.</p> + <div class="source"> + <pre>@PUT + @Path("{clusterId}") + public Response createCluster(@PathParam("clusterId") String clusterId, @DefaultValue("false") @QueryParam("recreate") String recreate, + @DefaultValue("false") @QueryParam("addCloudConfig") String addCloudConfig, String cloudConfigManifest) +</pre> + </div> + <p>Besides the enhanced cluster creation API, Helix also provides a set of cloud specific APIs in Java and REST that handles the get/add/update of cloud config. </p> + <ul> + <li>Create cluster and add meanwhile cloud config related information to ZK.</li> + </ul> + <div class="source"> + <pre>$ curl -X PUT -H "Content-Type: application/json" http://localhost:1234/admin/v2/clusters/myCluster?addCloudConfig=true -d ' +{ + "simpleFields" : + { + "CLOUD_ENABLED" : "true", + "CLOUD_PROVIDER": "AWS", + "CLOUD_ID" : "12345" + "CLOUD_INFO_SOURCE": {"http://169.254.169.254/"} + "CLOUD_INFO_PROCESSOR_NAME": "AWSCloudInformationProcesser" + } +}' +</pre> + </div> + <ul> + <li>Add cloud config to an existing cluster</li> + </ul> + <div class="source"> + <pre>$ curl -X PUT -H "Content-Type: application/json" http://localhost:1234/admin/v2/clusters/myCluster/cloudconfig -d ' +{ + "simpleFields" : + { + "CLOUD_ENABLED" : "true", + "CLOUD_PROVIDER": "AWS", + "CLOUD_ID" : "12345" + "CLOUD_INFO_SOURCE": {"http://169.254.169.254/"} + "CLOUD_INFO_PROCESSOR_NAME": "AWSCloudInformationProcesser" + } +}' +</pre> + </div> + <ul> + <li>Delete the cloud config of a cluster</li> + </ul> + <div class="source"> + <pre>$ curl -X DELETE http://localhost:1234/admin/v2/clusters/myCluster/cloudconfig +</pre> + </div> + <ul> + <li>Get the cloud config of a cluster</li> + </ul> + <div class="source"> + <pre>$ curl -X GET http://localhost:1234/admin/v2/clusters/myCluster/cloudconfig +</pre> + </div> + <ul> + <li>Update the cloud config of a cluster</li> + </ul> + <div class="source"> + <pre>$ curl -X POST -H "Content-Type: application/json" http://localhost:1234/admin/v2/clusters/myCluster/cloudconfig?command=update -d ' +{ + "simpleFields" : { + "CLOUD_ID" : "12345" + } +}' +</pre> + </div> + <ul> + <li>Delete some of the fields in the cloud config</li> + </ul> + <div class="source"> + <pre>$ curl -X POST -H "Content-Type: application/json" http://localhost:1234/admin/v2/clusters/myCluster/cloudconfig?command=delete -d ' +{ + "simpleFields" : { + "CLOUD_ID" : "12345" + } +}' +</pre> + </div> + </div> + </div> + <div class="section"> + <h4 id="Define_Cloud_Configs_at_Participant_Level">Define Cloud Configs at Participant Level</h4> + <p>At participant level, Helix allows users to provide detailed cloud properties, which is more related to the participantâs actions. For default value, Helix provides <a class="externalLink" href="https://github.com/apache/helix/blob/master/helix-core/src/main/resources/azure-cloud.properties";>Azure cloud properties</a>, including not only the default cluster level config values for Azure, like <tt>CLOUD_INFO_SOURCE</tt> and <tt>CLOUD_INFO_PROCESSOR_NAME</tt>, but also some participant specific values, such as http timeout when querying AIMS (Azure Instance Metadata Service) in Azure, max retry times, etc. </p> + <div class="source"> + <pre>cloud_info_source=http://169.254.169.254/metadata/instance?api-version=2019-06-04 +cloud_info_processor_name=AzureCloudInstanceInformationProcessor +cloud_max_retry=5 +connection_timeout_ms=5000 +request_timeout_ms=5000 +</pre> + </div> + <p>If users would like to use their customized config for participants, they can input the specific properties through <a class="externalLink" href="https://github.com/apache/helix/blob/master/helix-core/src/main/java/org/apache/helix/HelixManagerProperty.java";>Helix Manager Property</a> when composing <a class="externalLink" href="https://github.com/apache/helix/blob/master/helix-core/src/main/java/org/apache/helix/manager/zk/ZKHelixManager.java";>Zk Helix Manager</a>, which is passed into participants. <a class="externalLink" href="https://github.com/apache/helix/blob/master/helix-core/src/main/java/org/apache/helix/HelixManagerProperty.java";>Helix Manager Property</a> includes <a class="externalLink" href="https://github.com/apache/helix/blob/master/helix-core/src/main/java/org/apache/helix/HelixCloudProperty.java";>Helix Cloud Property</a> which includes commonly used cloud properties and also any kind of user defined cloud properties.</p> + <div class="source"> + <pre>public ZKHelixManager(String clusterName, String instanceName, InstanceType instanceType, + String zkAddress, HelixManagerStateListener stateListener, HelixManagerProperty helixManagerProperty) +</pre> + </div> + </div> + <div class="section"> + <h4 id="Implement_Cloud_Instance_Information_if_necessary">Implement Cloud Instance Information (if necessary)</h4> + <p>Helix has predefined a few fields in the interface of <a class="externalLink" href="https://github.com/apache/helix/blob/master/helix-core/src/main/java/org/apache/helix/api/cloud/CloudInstanceInformation.java";>CloudInstanceInformation</a> that are commonly used in participant. Users are free to define other fields in the instance metadata that they think are useful. </p> + <div class="source"> + <pre>public interface CloudInstanceInformation { + /** + * Get the the value of a specific cloud instance field by name + * @return the value of the field + */ + String get(String key); + + /** + * The enum contains all the required cloud instance field in Helix + */ + enum CloudInstanceField { + INSTANCE_NAME, + FAULT_DOMAIN, + INSTANCE_SET_NAME + } +} +</pre> + </div> + </div> + <div class="section"> + <h4 id="Implement_Cloud_Instance_Information_Processor_if_necessary">Implement Cloud Instance Information Processor (if necessary)</h4> + <p>Helix provides an interface to fetch and parse cloud instance information as follows. Helix makes the interface generic enough so that users may implement their own fetching and parsing logic with maximum freedom. </p> + <div class="source"> + <pre>/** + * Generic interface to fetch and parse cloud instance information + */ +public interface CloudInstanceInformationProcessor<T extends Object> { + + /** + * Get the raw cloud instance information + * @return raw cloud instance information + */ + List<T> fetchCloudInstanceInformation(); + + /** + * Parse the raw cloud instance information in responses and compose required cloud instance information + * @return required cloud instance information + */ + CloudInstanceInformation parseCloudInstanceInformation(List<T> responses); +} +</pre> + </div> + <p>Helix also implements an example processor for Azure in <a class="externalLink" href="https://github.com/apache/helix/blob/master/helix-core/src/main/java/org/apache/helix/cloud/azure/AzureCloudInstanceInformationProcessor.java";>AzureCloudInstanceInformationProcessor</a>. The implementation includes fetching and parsing Azure cloud instance information. The fetching function retrieves instance information from Azure AIMS, and the parsing function validates the response, and selects the fields needed for participant auto registration. If users would like to use Helix in an Azure environment, they do not need to implement it by themselves. </p> + <p>If users need to use Helix in another cloud environment, they can implement their own information processor. The implementation would be similar to Azure implementation, and the main difference would be in how to parse the response and retrieve interested fields. </p> + </div> + <div class="section"> + <h4 id="Config_Properly_for_Participant_Auto_Registration_to_Work">Config Properly for Participant Auto Registration to Work</h4> + <p>To make the participant auto registration work, users would need to make sure their cluster config is set properly. The most important one is the <tt>allowParticipantAutoJoin</tt> field in cluster config.</p> + <div class="source"> + <pre>{ + "id": "clusterName", + "listFields": {}, + "mapFields": {}, + "simpleFields": { + ...... + "allowParticipantAutoJoin": "true" + ...... + } +} +</pre> + </div> + <p>This field is used in participant manager logic as a prerequisite for participants to do auto registration. The detailed logic is shown in the following flow chart. The related code is in <a class="externalLink" href="https://github.com/apache/helix/blob/master/helix-core/src/main/java/org/apache/helix/manager/zk/ParticipantManager.java";>Participant Manager</a>.</p> + <p><img src="./images/ParticipantAutoRegistrationLogic.png" alt="Participant Auto Registration Logic" /></p> + <p>If the participant decides that it should do auto registration based on the config, it will first query cloud config and decide what environment it is in. Based on this information, the participant will call the corresponding cloud instance information processor. Then with all the information, especially the domain information, the participant can auto register to the cluster without any manual effort.</p> + </div> + </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-0.9.9.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> + <a href="Quickstart.html" title="Quick Start">Quick Start </a> + </li> + <li> + <a href="Tutorial.html" title="Tutorial">Tutorial </a> + </li> + <li> + <a href="../javadocs/0.9.9" 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 ©2020 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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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="Helix_Tutorial:_Controller"><a href="./Tutorial.html">Helix Tutorial</a>: Controller</h2> + </div> + <p>Next, let's implement the controller. This is the brain of the cluster. Helix makes sure there is exactly one active controller running the cluster.</p> + <div class="section"> + <h3 id="Start_a_Connection">Start a Connection</h3> + <p>The Helix manager requires the following parameters:</p> + <ul> + <li>clusterName: A logical name to represent the group of nodes</li> + <li>instanceName: A logical name of the process creating the manager instance. Generally this is host:port</li> + <li>instanceType: Type of the process. This can be one of the following types, in this case use CONTROLLER: + <ul> + <li>CONTROLLER: Process that controls the cluster, any number of controllers can be started but only one will be active at any given time</li> + <li>PARTICIPANT: Process that performs the actual task in the distributed system</li> + <li>SPECTATOR: Process that observes the changes in the cluster</li> + <li>ADMIN: To carry out system admin actions</li> + </ul></li> + <li>zkConnectString: Connection string to ZooKeeper. This is of the form host1:port1,host2:port2,host3:port3</li> + </ul> + <div class="source"> + <pre>manager = HelixManagerFactory.getZKHelixManager(clusterName, + instanceName, + instanceType, + zkConnectString); +</pre> + </div> + </div> + <div class="section"> + <h3 id="Controller_Code">Controller Code</h3> + <p>The Controller needs to know about all changes in the cluster. Helix takes care of this with the default implementation. If you need additional functionality, see GenericHelixController on how to configure the pipeline.</p> + <div class="source"> + <pre>manager = HelixManagerFactory.getZKHelixManager(clusterName, + instanceName, + InstanceType.CONTROLLER, + zkConnectString); +manager.connect(); +</pre> + </div> + <p>The snippet above shows how the controller is started. You can also start the controller using command line interface.</p> + <div class="source"> + <pre>cd helix/helix-core/target/helix-core-pkg/bin +./run-helix-controller.sh --zkSvr <Zookeeper ServerAddress (Required)> --cluster <Cluster name (Required)> +</pre> + </div> + </div> + <div class="section"> + <h3 id="Controller_Deployment_Modes">Controller Deployment Modes</h3> + <p>Helix provides multiple options to deploy the controller.</p> + <div class="section"> + <h4 id="STANDALONE">STANDALONE</h4> + <p>The Controller can be started as a separate process to manage a cluster. This is the recommended approach. However, 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 take over 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 the 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 participants.</p> + </div> + <div class="section"> + <h4 id="CONTROLLER_AS_A_SERVICE">CONTROLLER AS A SERVICE</h4> + <p>One of the cool features we added in Helix was to use a set of controllers to manage a large number of clusters.</p> + <p>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 just 3 controllers. Each controller can manage X/3 clusters. If any controller fails, the remaining two will manage X/2 clusters.</p> + <p>Next, let's implement the controller. This is the brain of the cluster. Helix makes sure there is exactly one active controller running the cluster.</p> + </div> + </div> + <div class="section"> + <h3 id="Start_the_Helix_agent">Start the Helix agent</h3> + <p>It requires the following parameters:</p> + <ul> + <li>clusterName: A logical name to represent the group of nodes</li> + <li>instanceName: A logical name of the process creating the manager instance. Generally this is host:port.</li> + <li>instanceType: Type of the process. This can be one of the following types, in this case use CONTROLLER: + <ul> + <li>CONTROLLER: Process that controls the cluster, any number of controllers can be started but only one will be active at any given time.</li> + <li>PARTICIPANT: Process that performs the actual task in the distributed system.</li> + <li>SPECTATOR: Process that observes the changes in the cluster.</li> + <li>ADMIN: To carry out system admin actions.</li> + </ul></li> + <li>zkConnectString: Connection string to Zookeeper. This is of the form host1:port1,host2:port2,host3:port3.</li> + </ul> + <div class="source"> + <pre> manager = HelixManagerFactory.getZKHelixManager(clusterName, + instanceName, + instanceType, + zkConnectString); +</pre> + </div> + </div> + <div class="section"> + <h3 id="Controller_Code">Controller Code</h3> + <p>The Controller needs to know about all changes in the cluster. Helix takes care of this with the default implementation. If you need additional functionality, see GenericHelixController on how to configure the pipeline.</p> + <div class="source"> + <pre> manager = HelixManagerFactory.getZKHelixManager(clusterName, + instanceName, + InstanceType.CONTROLLER, + zkConnectString); + manager.connect(); + GenericHelixController controller = new GenericHelixController(); + manager.addConfigChangeListener(controller); + manager.addLiveInstanceChangeListener(controller); + manager.addIdealStateChangeListener(controller); + manager.addExternalViewChangeListener(controller); + manager.addControllerListener(controller); +</pre> + </div> + <p>The snippet above shows how the controller is started. You can also start the controller using command line interface.</p> + <div class="source"> + <pre>cd helix/helix-core/target/helix-core-pkg/bin +./run-helix-controller.sh --zkSvr <Zookeeper ServerAddress (Required)> --cluster <Cluster name (Required)> +</pre> + </div> + </div> + <div class="section"> + <h3 id="Controller_Deployment_Modes">Controller Deployment Modes</h3> + <p>Helix provides multiple options to deploy the controller.</p> + <div class="section"> + <h4 id="STANDALONE">STANDALONE</h4> + <p>The Controller can be started as a separate process to manage a cluster. This is the recommended approach. However, 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 take over 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 participants.</p> + </div> + <div class="section"> + <h4 id="CONTROLLER_AS_A_SERVICE">CONTROLLER AS A SERVICE</h4> + <p>One of the cool features we added in Helix is to use a set of controllers to manage a large number of clusters.</p> + <p>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 just 3 controllers. Each controller can manage X/3 clusters. If any controller fails, the remaining two will manage X/2 clusters.</p> + </div> + </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-0.9.9.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> + <a href="Quickstart.html" title="Quick Start">Quick Start </a> + </li> + <li> + <a href="Tutorial.html" title="Tutorial">Tutorial </a> + </li> + <li> + <a href="../javadocs/0.9.9" 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 ©2020 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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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="Helix_Tutorial:_Customizing_Health_Checks"><a href="./Tutorial.html">Helix Tutorial</a>: Customizing Health Checks</h2> + </div> + <p>In this chapter, we'll learn how to customize health checks based on metrics of your distributed system.</p> + <div class="section"> + <h3 id="Health_Checks">Health Checks</h3> + <p>Note: <i>this in currently in development mode, not yet ready for production.</i></p> + <p>Helix provides the ability for each node in the system to report health metrics on a periodic basis.</p> + <p>Helix supports multiple ways to aggregate these metrics:</p> + <ul> + <li>SUM</li> + <li>AVG</li> + <li>EXPONENTIAL DECAY</li> + <li>WINDOW</li> + </ul> + <p>Helix persists the aggregated value only.</p> + <p>Applications can define a threshold on the aggregate values according to the SLAs, and when the SLA is violated Helix will fire an alert. Currently Helix only fires an alert, but in a future release we plan to use these metrics to either mark the node dead or load balance the partitions. This feature will be valuable for distributed systems that support multi-tenancy and have a large variation in work load patterns. In addition, this can be used to detect skewed partitions (hotspots) and rebalance the cluster.</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-0.9.9.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> + <a href="Quickstart.html" title="Quick Start">Quick Start </a> + </li> + <li> + <a href="Tutorial.html" title="Tutorial">Tutorial </a> + </li> + <li> + <a href="../javadocs/0.9.9" 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 ©2020 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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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="Helix_Tutorial:_Messaging"><a href="./Tutorial.html">Helix Tutorial</a>: Messaging</h2> + </div> + <p>In this chapter, we'll learn about messaging, a convenient feature in Helix for sending messages between nodes of a cluster. This is an interesting feature that is quite useful in practice. It is common that nodes in a distributed system require a mechanism to interact with each other.</p> + <div class="section"> + <h3 id="Example:_Bootstrapping_a_Replica">Example: Bootstrapping a Replica</h3> + <p>Consider a search system where the index replica starts up and it does not have an index. A typical solution is to get the index from a common location, or to copy the index from another replica.</p> + <p>Helix provides a messaging API for intra-cluster communication between nodes in the system. This API provides a mechanism to specify the message recipient in terms of resource, partition, and state rather than specifying hostnames. 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 the desired partition to bootstrap. Since Helix is aware of the global state of the system, it can send the message to the 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, such as data backups, log cleanup, etc. System Admins can also perform ad-hoc tasks, such as on-demand backups or a system command (such as rm -rf ;) across all nodes of the cluster</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 by process(es) that are active at the time of sending the message +// This means if the recipient is restarted after message is sent, it will not be processe. +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.DefaultMessagingService in the <a class="externalLink" href="http://helix.apache.org/javadocs/0.9.9/reference/org/apache/helix/messaging/DefaultMessagingService.html";>Javadocs</a> for more information.</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-0.9.9.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> + <a href="Quickstart.html" title="Quick Start">Quick Start </a> + </li> + <li> + <a href="Tutorial.html" title="Tutorial">Tutorial </a> + </li> + <li> + <a href="../javadocs/0.9.9" 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 ©2020 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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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="Helix_Tutorial:_Participant"><a href="./Tutorial.html">Helix Tutorial</a>: Participant</h2> + </div> + <p>In this chapter, we'll learn how to implement a <b>Participant</b>, which is a primary functional component of a distributed system.</p> + <div class="section"> + <h3 id="Start_a_Connection">Start a Connection</h3> + <p>The Helix manager is a common component that connects each system component with the controller.</p> + <p>It requires the following parameters:</p> + <ul> + <li>clusterName: A logical name to represent the group of nodes</li> + <li>instanceName: A logical name of the process creating the manager instance. Generally this is host:port</li> + <li>instanceType: Type of the process. This can be one of the following types, in this case, use PARTICIPANT + <ul> + <li>CONTROLLER: Process that controls the cluster, any number of controllers can be started but only one will be active at any given time</li> + <li>PARTICIPANT: Process that performs the actual task in the distributed system</li> + <li>SPECTATOR: Process that observes the changes in the cluster</li> + <li>ADMIN: To carry out system admin actions</li> + </ul></li> + <li>zkConnectString: Connection string to ZooKeeper. This is of the form host1:port1,host2:port2,host3:port3</li> + </ul> + <p>After the Helix manager instance is created, the only thing that needs to be registered is the state model factory. The methods of the state model will be called when controller sends transitions to the participant. In this example, weâll use the OnlineOffline factory. Other options include:</p> + <ul> + <li>MasterSlaveStateModelFactory</li> + <li>LeaderStandbyStateModelFactory</li> + <li>BootstrapHandler</li> + </ul> + <div class="source"> + <pre>manager = HelixManagerFactory.getZKHelixManager(clusterName, + instanceName, + InstanceType.PARTICIPANT, + zkConnectString); +StateMachineEngine stateMach = manager.getStateMachineEngine(); + +//create a stateModelFactory that returns a statemodel object for each partition. +stateModelFactory = new OnlineOfflineStateModelFactory(); +stateMach.registerStateModelFactory(stateModelType, stateModelFactory); +manager.connect(); +</pre> + </div> + </div> + <div class="section"> + <h3 id="Example_State_Model_Factory">Example State Model Factory</h3> + <p>Helix doesn't know what it means to change from OFFLINE-->ONLINE or ONLINE-->OFFLINE. The following code snippet shows where you insert your system logic for these two state transitions.</p> + <div class="source"> + <pre>public class OnlineOfflineStateModelFactory extends + StateModelFactory<StateModel> { + @Override + public StateModel createNewStateModel(String stateUnitKey) { + OnlineOfflineStateModel stateModel = new OnlineOfflineStateModel(); + return stateModel; + } + @StateModelInfo(states = "{'OFFLINE','ONLINE'}", initialState = "OFFINE") + public static class OnlineOfflineStateModel extends StateModel { + @Transition(from = "OFFLINE", to = "ONLINE") + public void onBecomeOnlineFromOffline(Message message, + NotificationContext context) { + System.out.println("OnlineOfflineStateModel.onBecomeOnlineFromOffline()"); + + //////////////////////////////////////////////////////////////////////////////////////////////// + // Application logic to handle transition // + // For example, you might start a service, run initialization, etc // + //////////////////////////////////////////////////////////////////////////////////////////////// + } + + @Transition(from = "ONLINE", to = "OFFLINE") + public void onBecomeOfflineFromOnline(Message message, + NotificationContext context) { + System.out.println("OnlineOfflineStateModel.onBecomeOfflineFromOnline()"); + + //////////////////////////////////////////////////////////////////////////////////////////////// + // Application logic to handle transition // + // For example, you might shutdown a service, log this event, or change monitoring settings // + //////////////////////////////////////////////////////////////////////////////////////////////// + } + } +} +</pre> + </div> + </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-0.9.9.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> + <a href="Quickstart.html" title="Quick Start">Quick Start </a> + </li> + <li> + <a href="Tutorial.html" title="Tutorial">Tutorial </a> + </li> + <li> + <a href="../javadocs/0.9.9" 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 ©2020 <a href="http://www.apache.org/";>The Apache Software Foundation</a>. 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