The ResourceManager service tracks a cluster's resources and schedules YARN applications. Configure high availability for the ResourceManager so that the failure of the ResourceManager service is not a single point of failure for the cluster. The high availability of ResourceManager is based on the cluster configuration of the restart, recovery, and failover features.
By default, the Warden attempts to restart a failed service three times. You can configure the frequency that Warden attempts to restart failed services before initializing failover in the warden.conf file. For more information, see warden.conf.
When a ResourceManager restarts or fails over, the active ResourceManager can recover the state of the previously running ResourceManager. By default, ResourceManager recovery is enabled and it uses the FileSystemRMStateStore implementation to store the ResourceManager state in the MapR-FS. You can configure the ResourceManager to have no recovery or you can enable the recovery. You can also configure the state store implementation that you want to use. For more information, see Recovery for the ResourceManager.
When a ResourceManager fails, the cluster can fail over the ResourceManager process to another node. To configure failover, the cluster must have one or more nodes with the ResourceManager role.
Starting in Version 4.0.2, zero configuration failover provides automatic failover without requiring that you specify the ResourceManager nodes when you run configure.sh. It also does not require any further configuration to yarn-site.xml.
Upgrade any client nodes to the 4.0.2 client to ensure proper communication with the ResourceManager service. Earlier versions of the MapR client do not support the zero configuration feature.
You can select one of the following failover implementations when you use the configure.sh utility to configure each node:
- Zero Configuration Failover. With zero configuration failover, the ResourceManager process only runs on one node in the cluster. When the active ResourceManager fails, one of the standby ResourceManager nodes automatically loads the working state from the state store and continues providing services to the cluster.
Zero configuration failover is the default, recommended setting for the following reasons:
- Only one ResourceManager process consumes cluster resources. With the manual or automatic failover option, the active and standby ResourceManagers consume cluster resources.
- Warden initiates failover automatically. With the manual failover, you need to manually run the yarn rmadmin command for failover to occur.
- Simplified clients connectivity. Clients identify the active ResourceManager with a single request to the Zookeeper. With the manual or automatic failover option, ResourceManager clients connect to each ResourceManager in a round-robin fashion until they locate the active ResourceManager; this results in delays when launching or querying jobs.
- Consistent Configuration. All cluster nodes and clients can use the same yarn-site.xml configuration file. With manual or automatic failover, you must maintain a customized yarn-site.xml file for each node that runs the ResourceManager.
- Manual or Automatic Failover. With manual failover or automatic failover, one active ResourceManager and one or more standby Resource Managers run in the cluster. The standby ResourceManager nodes run the ResourceManager process without loading the working state. When the active ResourceManager fails, one of the standby ResourceManager nodes can load the working state from the state store and continue providing services to the cluster. For more information, see Manual or Automatic Failover for the ResourceManager.