Configuration and environment overrides

The cluster definition also supports overriding configuration properties and environment variables, 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 (such as the ports) 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 zoo.cfg and security.properties files.

Overriding entries in zoo.cfg

For example, if you want to set the 4lw.commands.whitelist to allow the ruok administrative command, it can be configured in the ZookeeperCluster resource like so:

servers:
  roleGroups:
    default:
      configOverrides:
        zoo.cfg:
          4lw.commands.whitelist: "srvr, ruok"
      replicas: 1

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

servers:
  configOverrides:
    zoo.cfg:
      4lw.commands.whitelist: "srvr, ruok"
  roleGroups:
    default:
      replicas: 1

All property values must be strings.

For a full list of configuration options refer to the Apache ZooKeeper Configuration Reference.

Overriding entries in security.properties

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 its 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 3.8.1, Apache ZooKeeper always requires up-to-date IP addresses to maintain its quorum. To guarantee this, the negative DNS cache of the JVM needs to be disabled. This can be achieved by setting the TTL of entries in the negative cache to zero, like this:

  servers:
    configOverrides:
      security.properties:
        networkaddress.cache.ttl: "5"
        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

In a similar fashion, environment variables can be (over)written. For example per role group:

servers:
  roleGroups:
    default:
      envOverrides:
        MY_ENV_VAR: "MY_VALUE"
      replicas: 1

or per role:

servers:
  envOverrides:
    MY_ENV_VAR: "MY_VALUE"
  roleGroups:
    default:
      replicas: 1

Pod overrides

The ZooKeeper operator also supports 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.