Module org.elasticsearch.server
Package org.elasticsearch.features

Interface FeatureSpecification

All Known Implementing Classes:
BulkFeatures, ClusterRerouteFeatures, ClusterStatsFeatures, IndexFeatures, InfrastructureFeatures, MapperFeatures, RetrieversFeatures, RoutingFeatures, ScriptFeatures, SearchFeatures, SynonymFeatures
public interface FeatureSpecification
Specifies one or more features that are supported by this node.

Features are published as part of node information in cluster state. Code can check if all nodes in a cluster support a feature using FeatureService.clusterHasFeature(org.elasticsearch.cluster.ClusterState, org.elasticsearch.features.NodeFeature). Once all nodes in a cluster support a feature, other nodes are blocked from joining that cluster unless they also support that feature (this is known as the 'feature ratchet'). So once a feature is supported by a cluster, it will always be supported by that cluster in the future.

The only situation where features can be removed is on a compatibility boundary (normally a new major version). Because a new major version can only form a cluster with the highest minor of the previous major, any features introduced before that point can be assumed to always be present on that cluster. The feature itself can be removed by marking it as assumed by NodeFeature.assumedAfterNextCompatibilityBoundary(), in the last minor, and then removing it and associated conditions in the new major version.

The feature information in cluster state should not normally be directly accessed. All feature checks should be done through FeatureService to ensure that Elasticsearch's guarantees on the introduction of new functionality are followed; that is, new functionality is not enabled until all nodes in the cluster support it.

Note: FeatureSpecifications are loaded as service providers, however tests are not fully modularized yet. Make sure to also register new specifications in META-INF/services/org.elasticsearch.features.FeatureSpecification, so they are available in tests as well.

  • Method Summary

    Modifier and Type
    Method
    Description
    default Set<NodeFeature>
    getFeatures()
    Returns a set of features that this node supports.
    default Set<NodeFeature>
    getTestFeatures()
    Returns a set of test features that this node supports.

  • Method Details

    • getFeatures

      default Set<NodeFeature> getFeatures()
      Returns a set of features that this node supports.

    • getTestFeatures

      default Set<NodeFeature> getTestFeatures()
      Returns a set of test features that this node supports.

      These features will only be exposed if the tests.testfeatures.enabled system property is set. This should only be used when deploying test clusters.