YARN-7598. Document how to use classpath isolation for aux-services in YARN. Contributed by Xuan Gong.
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Junping Du
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@ -87,4 +87,51 @@ Step 4. Auxiliary services.
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* NodeManagers in a YARN cluster can be configured to run auxiliary services. For a completely functional NM restart, YARN relies on any auxiliary service configured to also support recovery. This usually includes (1) avoiding usage of ephemeral ports so that previously running clients (in this case, usually containers) are not disrupted after restart and (2) having the auxiliary service itself support recoverability by reloading any previous state when NodeManager restarts and reinitializes the auxiliary service.
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* NodeManagers in a YARN cluster can be configured to run auxiliary services. For a completely functional NM restart, YARN relies on any auxiliary service configured to also support recovery. This usually includes (1) avoiding usage of ephemeral ports so that previously running clients (in this case, usually containers) are not disrupted after restart and (2) having the auxiliary service itself support recoverability by reloading any previous state when NodeManager restarts and reinitializes the auxiliary service.
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* A simple example for the above is the auxiliary service 'ShuffleHandler' for MapReduce (MR). ShuffleHandler respects the above two requirements already, so users/admins don't have do anything for it to support NM restart: (1) The configuration property **mapreduce.shuffle.port** controls which port the ShuffleHandler on a NodeManager host binds to, and it defaults to a non-ephemeral port. (2) The ShuffleHandler service also already supports recovery of previous state after NM restarts.
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* A simple example for the above is the auxiliary service 'ShuffleHandler' for MapReduce (MR). ShuffleHandler respects the above two requirements already, so users/admins don't have to do anything for it to support NM restart: (1) The configuration property **mapreduce.shuffle.port** controls which port the ShuffleHandler on a NodeManager host binds to, and it defaults to a non-ephemeral port. (2) The ShuffleHandler service also already supports recovery of previous state after NM restarts.
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Auxiliary Service Classpath Isolation
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-------------------------------------
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### Introduction
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To launch auxiliary services on a NodeManager, users have to add their jar to NodeManager's classpath directly, thus put them on the system classloader. But if multiple versions of the plugin are present on the classpath, there is no control over which version actually gets loaded. Or if there are any conflicts between the dependencies introduced by the auxiliary services and the NodeManager itself, they can break the NodeManager, the auxiliary services, or both. To solve this issue, we can instantiate auxiliary services using a classloader that is different from the system classloader.
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### Configuration
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This section describes the configuration variables for aux-service classpath isolation.
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The following settings need to be set in *yarn-site.xml*.
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|Configuration Name | Description |
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|:---- |:---- |
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| `yarn.nodemanager.aux-services.%s.classpath` | Provide local directory which includes the related jar file as well as all the dependencies’ jar file. We could specify the single jar file or use ${local_dir_to_jar}/* to load all jars under the dep directory. |
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| `yarn.nodemanager.aux-services.%s.remote-classpath` | Provide remote absolute or relative path to jar file(We also support zip, tar.gz, tgz, tar and gz files as well). For the same aux-service class, we can only specify one of the configurations: yarn.nodemanager.aux-services.%s.classpath or yarn.nodemanager.aux-services.%s.remote-classpath. The YarnRuntimeException will be thrown. Please also make sure that the owner of the jar file must be the same as the NodeManager user and the permbits should satisfy (permbits & 0022)==0 (such as 600, it's not writable by group or other).|
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| `yarn.nodemanager.aux-services.%s.system-classes` | Normally, we do not need to set this configuration. The class would be loaded from customized classpath if it does not belongs to system-classes. For example, by default, the package org.apache.hadoop is in the system-classes, if your class CustomAuxService is in the package org.apache.hadoop, it would not be loaded from customized classpath. To solve this, either we could change the package for CustomAuxService, or configure our own system-classes which exclude org.apache.hadoop. |
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### Configuration Examples
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<property>
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<name>yarn.nodemanager.aux-services</name>
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<value>mapreduce_shuffle,CustomAuxService</value>
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</property>
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<property>
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<name>yarn.nodemanager.aux-services.CustomAuxService.classpath</name>
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<value>${local_dir_to_jar}/CustomAuxService.jar</value>
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</property>
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<!--
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<property>
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<name>yarn.nodemanager.aux-services.CustomAuxService.remote-classpath</name>
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<value>${remote-dir_to_jar}/CustomAuxService.jar</value>
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</property>
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-->
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<property>
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<name>yarn.nodemanager.aux-services.CustomAuxService.class</name>
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<value>org.aux.CustomAuxService</value>
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</property>
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<property>
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<name>yarn.nodemanager.aux-services.mapreduce_shuffle.class</name>
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<value>org.apache.hadoop.mapred.ShuffleHandler</value>
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</property>
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