Configuration & 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 following files:

server.properties
security.properties

For example, if you want to set the auto.create.topics.enable to disable automatic topic creation, it can be configured in the KafkaCluster resource like so:

brokers:
  roleGroups:
    default:
      configOverrides:
        server.properties:
          auto.create.topics.enable: "false"
      replicas: 1

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

brokers:
  configOverrides:
    server.properties:
      auto.create.topics.enable: "false"
  roleGroups:
    default:
      replicas: 1

All override property values must be strings.

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

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 3.4.0 Apache Kafka performs poorly if the positive cache is disabled. To cache resolved host names, you can configure the TTL of entries in the positive cache like this:

  brokers:
    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

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