Module org.elasticsearch.server
Package org.elasticsearch.reservedstate

Interface ReservedClusterStateHandler<T>

All Known Implementing Classes:
ReservedClusterSettingsAction, ReservedComposableIndexTemplateAction, ReservedPipelineAction, ReservedRepositoryAction
public interface ReservedClusterStateHandler<T>
Base interface used for implementing 'operator mode' cluster state updates.

Reserving cluster state, for file based settings and modules/plugins, requires that we have a separate update handler interface that is different than the REST handlers. This interface class declares the basic contract for implementing cluster state update handlers that result in a cluster state that is effectively immutable by the REST handlers. The only way the reserved cluster state can be updated is through the 'operator mode' actions, e.g. updating the file settings.

  • Method Details

    • name

      String name()
      Unique identifier for the handler.

      The handler name is a unique identifier that is matched to a section in a cluster state update content. The reserved cluster state updates are done as a single cluster state update and the cluster state is typically supplied as a combined content, unlike the REST handlers. This name must match a desired content key name in the combined cluster state update, e.g. "ilm" or "cluster_settings" (for persistent cluster settings update).

      Returns:
      a String with the handler name, e.g "ilm".

    • transform

      TransformState transform(Object source, TransformState prevState) throws Exception
      The transformation method implemented by the handler.

      The transform method of the handler should apply the necessary changes to the cluster state as it normally would in a REST handler. One difference is that the transform method in an reserved state handler must perform all CRUD operations of the cluster state in one go. For that reason, we supply a wrapper class to the cluster state called TransformState, which contains the current cluster state as well as any previous keys set by this handler on prior invocation.

      Parameters:
      source - The parsed information specific to this handler from the combined cluster state content
      prevState - The previous cluster state and keys set by this handler (if any)
      Returns:
      The modified state and the current keys set by this handler
      Throws:
      Exception

    • dependencies

      default Collection<String> dependencies()
      List of dependent handler names for this handler.

      Sometimes certain parts of the cluster state cannot be created/updated without previously setting other cluster state components, e.g. composable templates. Since the reserved cluster state handlers are processed in random order by the ReservedClusterStateService, this method gives an opportunity to any reserved handler to declare other state handlers it depends on. Given dependencies exist, the ReservedClusterStateService will order those handlers such that the handlers that are dependent on are processed first.

      Returns:
      a collection of reserved state handler names

    • optionalDependencies

      default Collection<String> optionalDependencies()
      List of optional dependent handler names for this handler.

      These are dependent handlers which may or may not exist for this handler to be processed. If the optional dependency exists, then they are simply ordered to be merged into the cluster state before this handler.

      Returns:
      a collection of optional reserved state handler names

    • validate

      default void validate(MasterNodeRequest<?> request)
      Generic validation helper method that throws consistent exception for all handlers.

      All implementations of ReservedClusterStateHandler should call the request validate method, by calling this default implementation. To aid in any special validation logic that may need to be implemented by the reserved cluster state handler we provide this convenience method.

      Parameters:
      request - the master node request that we base this reserved state handler on

    • fromXContent

      T fromXContent(XContentParser parser) throws IOException
      The parse content method which is called during parsing of file based content.

      The immutable state can be provided as XContent, which means that each handler needs to implement a method to convert an XContent to an object it can consume later in transform

      Parameters:
      parser - the XContent parser we are parsing from
      Returns:
      Throws:
      IOException