YARN-1696. Added documentation for ResourceManager fail-over. Contributed by Karthik Kambatla, Masatake Iwasaki, Tsuyoshi OZAWA.
svn merge --ignore-ancestry -c 1591416 ../../trunk/ git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-2@1591417 13f79535-47bb-0310-9956-ffa450edef68
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Vinod Kumar Vavilapalli
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@ -101,6 +101,7 @@
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<item name="Capacity Scheduler" href="hadoop-yarn/hadoop-yarn-site/CapacityScheduler.html"/>
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<item name="Fair Scheduler" href="hadoop-yarn/hadoop-yarn-site/FairScheduler.html"/>
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<item name="ResourceManager Restart" href="hadoop-yarn/hadoop-yarn-site/ResourceManagerRestart.html"/>
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<item name="ResourceManager HA" href="hadoop-yarn/hadoop-yarn-site/ResourceManagerHA.html"/>
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<item name="Web Application Proxy" href="hadoop-yarn/hadoop-yarn-site/WebApplicationProxy.html"/>
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<item name="YARN Timeline Server" href="hadoop-yarn/hadoop-yarn-site/TimelineServer.html"/>
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<item name="Writing YARN Applications" href="hadoop-yarn/hadoop-yarn-site/WritingYarnApplications.html"/>
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@ -77,6 +77,9 @@ Release 2.4.1 - UNRELEASED
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YARN-1892. Improved some logs in the scheduler. (Jian He via zjshen)
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YARN-1696. Added documentation for ResourceManager fail-over. (Karthik
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Kambatla, Masatake Iwasaki, Tsuyoshi OZAWA via vinodkv)
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OPTIMIZATIONS
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BUG FIXES
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@ -0,0 +1,234 @@
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~~ Licensed under the Apache License, Version 2.0 (the "License");
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~~ you may not use this file except in compliance with the License.
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~~ You may obtain a copy of the License at
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~~
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~~ http://www.apache.org/licenses/LICENSE-2.0
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~~
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~~ Unless required by applicable law or agreed to in writing, software
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~~ distributed under the License is distributed on an "AS IS" BASIS,
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~~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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~~ See the License for the specific language governing permissions and
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~~ limitations under the License. See accompanying LICENSE file.
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---
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ResourceManager High Availability
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---
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---
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${maven.build.timestamp}
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ResourceManager High Availability
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\[ {{{./index.html}Go Back}} \]
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%{toc|section=1|fromDepth=0}
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* Introduction
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This guide provides an overview of High Availability of YARN's ResourceManager,
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and details how to configure and use this feature. The ResourceManager (RM)
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is responsible for tracking the resources in a cluster, and scheduling
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applications (e.g., MapReduce jobs). Prior to Hadoop 2.4, the ResourceManager
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is the single point of failure in a YARN cluster. The High Availability
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feature adds redundancy in the form of an Active/Standby ResourceManager pair
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to remove this otherwise single point of failure.
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* Architecture
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[images/rm-ha-overview.png] Overview of ResourceManager High Availability
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** RM Failover
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ResourceManager HA is realized through an Active/Standby architecture - at
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any point of time, one of the RMs is Active, and one or more RMs are in
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Standby mode waiting to take over should anything happen to the Active.
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The trigger to transition-to-active comes from either the admin (through CLI)
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or through the integrated failover-controller when automatic-failover is
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enabled.
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*** Manual transitions and failover
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When automatic failover is not enabled, admins have to manually transition
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one of the RMs to Active. To failover from one RM to the other, they are
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expected to first transition the Active-RM to Standby and transition a
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Standby-RM to Active. All this can be done using the "<<<yarn rmadmin>>>"
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CLI.
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*** Automatic failover
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The RMs have an option to embed the Zookeeper-based ActiveStandbyElector to
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decide which RM should be the Active. When the Active goes down or becomes
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unresponsive, another RM is automatically elected to be the Active which
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then takes over. Note that, there is no need to run a separate ZKFC daemon
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as is the case for HDFS because ActiveStandbyElector embedded in RMs acts
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as a failure detector and a leader elector instead of a separate ZKFC
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deamon.
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*** Client, ApplicationMaster and NodeManager on RM failover
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When there are multiple RMs, the configuration (yarn-site.xml) used by
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clients and nodes is expected to list all the RMs. Clients,
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ApplicationMasters (AMs) and NodeManagers (NMs) try connecting to the RMs in
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a round-robin fashion until they hit the Active RM. If the Active goes down,
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they resume the round-robin polling until they hit the "new" Active.
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This default retry logic is implemented as
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<<<org.apache.hadoop.yarn.client.ConfiguredRMFailoverProxyProvider>>>.
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You can override the logic by
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implementing <<<org.apache.hadoop.yarn.client.RMFailoverProxyProvider>>> and
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setting the value of <<<yarn.client.failover-proxy-provider>>> to
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the class name.
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** Recovering prevous active-RM's state
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With the {{{./ResourceManagerRestart.html}ResourceManger Restart}} enabled,
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the RM being promoted to an active state loads the RM internal state and
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continues to operate from where the previous active left off as much as
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possible depending on the RM restart feature. A new attempt is spawned for
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each managed application previously submitted to the RM. Applications can
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checkpoint periodically to avoid losing any work. The state-store must be
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visible from the both of Active/Standby RMs. Currently, there are two
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RMStateStore implementations for persistence - FileSystemRMStateStore
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and ZKRMStateStore. The <<<ZKRMStateStore>>> implicitly allows write access
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to a single RM at any point in time, and hence is the recommended store to
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use in an HA cluster. When using the ZKRMStateStore, there is no need for a
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separate fencing mechanism to address a potential split-brain situation
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where multiple RMs can potentially assume the Active role.
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* Deployment
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** Configurations
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Most of the failover functionality is tunable using various configuration
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properties. Following is a list of required/important ones. yarn-default.xml
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carries a full-list of knobs. See
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{{{../hadoop-yarn-common/yarn-default.xml}yarn-default.xml}}
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for more information including default values.
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See {{{./ResourceManagerRestart.html}the document for ResourceManger
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Restart}} also for instructions on setting up the state-store.
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*-------------------------+----------------------------------------------+
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|| Configuration Property || Description |
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*-------------------------+----------------------------------------------+
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| yarn.resourcemanager.zk-address | |
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| | Address of the ZK-quorum.
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| | Used both for the state-store and embedded leader-election.
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*-------------------------+----------------------------------------------+
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| yarn.resourcemanager.ha.enabled | |
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| | Enable RM HA
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*-------------------------+----------------------------------------------+
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| yarn.resourcemanager.ha.rm-ids | |
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| | List of logical IDs for the RMs. |
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| | e.g., "rm1,rm2" |
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*-------------------------+----------------------------------------------+
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| yarn.resourcemanager.hostname.<rm-id> | |
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| | For each <rm-id>, specify the hostname the |
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| | RM corresponds to. Alternately, one could set each of the RM's service |
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| | addresses. |
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*-------------------------+----------------------------------------------+
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| yarn.resourcemanager.ha.id | |
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| | Identifies the RM in the ensemble. This is optional; |
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| | however, if set, admins have to ensure that all the RMs have their own |
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| | IDs in the config |
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*-------------------------+----------------------------------------------+
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| yarn.resourcemanager.ha.automatic-failover.enabled | |
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| | Enable automatic failover; |
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| | By default, it is enabled only when HA is enabled. |
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*-------------------------+----------------------------------------------+
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| yarn.resourcemanager.ha.automatic-failover.embedded | |
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| | Use embedded leader-elector |
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| | to pick the Active RM, when automatic failover is enabled. By default, |
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| | it is enabled only when HA is enabled. |
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*-------------------------+----------------------------------------------+
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| yarn.resourcemanager.cluster-id | |
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| | Identifies the cluster. Used by the elector to |
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| | ensure an RM doesn't take over as Active for another cluster. |
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*-------------------------+----------------------------------------------+
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| yarn.client.failover-proxy-provider | |
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| | The class to be used by Clients, AMs and NMs to failover to the Active RM. |
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*-------------------------+----------------------------------------------+
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| yarn.client.failover-max-attempts | |
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| | The max number of times FailoverProxyProvider should attempt failover. |
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*-------------------------+----------------------------------------------+
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| yarn.client.failover-sleep-base-ms | |
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| | The sleep base (in milliseconds) to be used for calculating |
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| | the exponential delay between failovers. |
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*-------------------------+----------------------------------------------+
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| yarn.client.failover-sleep-max-ms | |
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| | The maximum sleep time (in milliseconds) between failovers |
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*-------------------------+----------------------------------------------+
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| yarn.client.failover-retries | |
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| | The number of retries per attempt to connect to a ResourceManager. |
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*-------------------------+----------------------------------------------+
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| yarn.client.failover-retries-on-socket-timeouts | |
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| | The number of retries per attempt to connect to a ResourceManager on socket timeouts. |
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*-------------------------+----------------------------------------------+
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*** Sample configurations
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Here is the sample of minimal setup for RM failover.
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+---+
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<property>
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<name>yarn.resourcemanager.ha.enabled</name>
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<value>true</value>
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</property>
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<property>
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<name>yarn.resourcemanager.cluster-id</name>
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<value>cluster1</value>
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</property>
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<property>
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<name>yarn.resourcemanager.ha.rm-ids</name>
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<value>rm1,rm2</value>
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</property>
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<property>
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<name>yarn.resourcemanager.hostname.rm1</name>
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<value>master1</value>
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</property>
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<property>
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<name>yarn.resourcemanager.hostname.rm2</name>
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<value>master2</value>
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</property>
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<property>
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<name>yarn.resourcemanager.zk-address</name>
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<value>zk1:2181,zk2:2181,zk3:2181</value>
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</property>
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+---+
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** Admin commands
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<<<yarn rmadmin>>> has a few HA-specific command options to check the health/state of an
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RM, and transition to Active/Standby.
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Commands for HA take service id of RM set by <<<yarn.resourcemanager.ha.rm-ids>>>
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as argument.
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+---+
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$ yarn rmadmin -getServiceState rm1
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active
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$ yarn rmadmin -getServiceState rm2
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standby
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+---+
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If automatic failover is enabled, you can not use manual transition command.
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+---+
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$ yarn rmadmin -transitionToStandby rm1
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Automatic failover is enabled for org.apache.hadoop.yarn.client.RMHAServiceTarget@1d8299fd
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Refusing to manually manage HA state, since it may cause
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a split-brain scenario or other incorrect state.
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If you are very sure you know what you are doing, please
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specify the forcemanual flag.
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+---+
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See {{{./YarnCommands.html}YarnCommands}} for more details.
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** ResourceManager Web UI services
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Assuming a standby RM is up and running, the Standby automatically redirects
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all web requests to the Active, except for the "About" page.
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** Web Services
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Assuming a standby RM is up and running, RM web-services described at
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{{{./ResourceManagerRest.html}ResourceManager REST APIs}} when invoked on
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a standby RM are automatically redirected to the Active RM.
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