Configuration, environment and Pod overrides

The HBase Stacklet definition also supports overriding configuration properties, environment variables and Pod specs, either per role or per role group, where the more specific override (role group) has precedence over the less specific one (role).

Overriding certain properties which are set by operator can interfere with the operator and can lead to problems.

Configuration properties

For a role or role group, at the same level of config, you can specify: configOverrides for the following files:

  • hbase-site.xml

  • hbase-env.sh

  • security.properties

hdfs-site.xml is not listed here, the file is always taken from the referenced HDFS cluster. If you want to modify it, take a look at HDFS configuration overrides.

For example, if you want to set the hbase.rest.threads.min to 4 and the HBASE_HEAPSIZE to two GB adapt the restServers section of the cluster resource like so:

restServers:
  roleGroups:
    default:
      config: {}
      configOverrides:
        hbase-site.xml:
          hbase.rest.threads.min: "4"
        hbase-env.sh:
          HBASE_HEAPSIZE: "2G"
      replicas: 1

Just as for the config, it is possible to specify this at role level as well:

restServers:
  configOverrides:
    hbase-site.xml:
      hbase.rest.threads.min: "4"
    hbase-env.sh:
      HBASE_HEAPSIZE: "2G"
  roleGroups:
    default:
      config: {}
      replicas: 1

All override property values must be strings. The properties will be formatted and escaped correctly into the XML file, respectively inserted as is into the hbase-env.sh file.

For a full list of configuration options we refer to the HBase configuration documentation.

The security.properties file

The security.properties file is used to configure JVM security properties. It is very seldom that users need to tweak any of these, but there is one use-case that stands out, and that users need to be aware of: the JVM DNS cache.

The JVM manages it’s own cache of successfully resolved host names as well as a cache of host names that cannot be resolved. Some products of the Stackable platform are very sensible to the contents of these caches and their performance is heavily affected by them. As of version 3.4.12, Apache Hbase performs poorly if the positive cache is disabled. To cache resolved host names, and thus speeding up Hbase queries you can configure the TTL of entries in the positive cache like this:

  masters:
    configOverrides:
      security.properties:
        networkaddress.cache.ttl: "5"
        networkaddress.cache.negative.ttl: "0"
  regionServers:
    configOverrides:
      security.properties:
        networkaddress.cache.ttl: "10"
        networkaddress.cache.negative.ttl: "0"
  restServers:
    configOverrides:
      security.properties:
        networkaddress.cache.ttl: "30"
        networkaddress.cache.negative.ttl: "0"
The operator configures DNS caching by default as shown in the example above.

For details on the JVM security see https://docs.oracle.com/en/java/javase/11/security/java-security-overview1.html

Environment variables

The HBaseCluster Stacklet does not support environment variable overrides with the envOverrides key like other Stacklets, but you can set environment variables in the hbase-env.sh file as described in the previous section.

Pod overrides

The HBase Stacklet and operator also support Pod overrides, allowing you to override any property that you can set on a Kubernetes Pod. Read the Pod overrides documentation to learn more about this feature.