CDH HDFS HA Support

CDH HDFS HA Support

https://blueprints.launchpad.net/sahara/+spec/cdh-ha-support

This blueprint aims to implement HDFS High-Availability (HA) for Cloudra plugin.

Problem description

Currently Cloudera plugin does not support HA for services. We plan to implement HDFS HA as the first step. HA for Yarn and other services will be the later steps.

Proposed change

The implementation of the HDFS HA will be done via CM API enable_nn_ha(). This API will help us enable HDFS HA by giving several info augments.

CDH 5 only supports Quorum-based Storage as the only HA implementation, so we will only implement this. To achieve this, we need to add a Standby NameNode, and several JournalNodes. The JournalNode number should be odd and at least 3. When HDFS HA is enabled, SecondaryNameNode will not be used. So we can reuse the node for SecondaryNameNode for StandbyNameNode.

HDFS HA has several hardware constraints (see the reference link). However, for all resources are virtual in Openstack, we will only require NameNode and StandbyNameNode are on different physical hosts.

Overall, we will implement HDFS as below:

  • Add a role JournalNode.
  • If JournalNode was selected by user (cluster admin), then HA will be enabled.
  • If HA is enabled, we will validate whether JournalNode number meet requirements.
  • JournalNode roles will not be really created during cluster creation. In fact they will be used as parameters of CM API enable_nn_ha.
  • If HA is enabled, we will use SecondaryNameNode as the StandbyNameNode.
  • If HA is enabled, we will set Anti-affinity to make sure NameNode and SecondaryNameNode will not be on the same physical host.
  • If HA is enabled, Zookeeper service is required in the cluster.
  • After the cluster was started, we will call enable_nn_ha to enable HDFS HA.
  • If HA is enabled, in Oozie workflow xml file, we will give nameservice name instead of the NameNode name in method get_name_node_uri. So that the cluster can determine by itself which NameNode is active.

Alternatives

None.

Data model impact

None.

REST API impact

None.

Other end user impact

None.

Deployer impact

None.

Developer impact

None.

Sahara-image-elements impact

None.

Sahara-dashboard / Horizon impact

None.

Implementation

Assignee(s)

Primary assignee:
Ken Chen

Work Items

Changes will be only in sahara/plugins/cdh directory. We will only do this based on CDH 5.4.0 at this stage. CDH 5.0.0 and CDH 5.3.0 plugins will not be supported. Changes were described in the Proposed change section.

Dependencies

None.

Testing

We will only do primitive checks: create a Cloudera cluster with HDFS HA, and see whether it is active.

Documentation Impact

The documentation needs to be updated with information about enabling CDH HDFS HA.

References

  • NameNode HA with QJM <http://www.edureka.co/blog/namenode-high-availability-with-quorum-journal-manager-qjm/>
  • Introduction to HDFS HA <http://www.cloudera.com/content/cloudera/en/documentation/core/latest/topics/cdh_hag_hdfs_ha_intro.html>
  • Enable HDFS HA Using Cloudera Manager <http://www.cloudera.com/content/cloudera/en/documentation/core/latest/topics/cdh_hag_hdfs_ha_enabling.html#cmug_topic_5_12_unique_1>
  • Configuring Hardware for HDFS HA <http://www.cloudera.com/content/cloudera/en/documentation/core/latest/topics/cdh_hag_hdfs_ha_hardware_config.html>
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