elastic/elasticsearch · error · RuntimeException

Failed to determine indexMode for data stream: {}

Error message

Failed to determine indexMode for data stream: {}

What it means

Thrown by TransportGetDataStreamsAction while resolving the index mode of a data stream when resolveMode throws an IOException (template parsing, settings merge, or mode computation failure). It is wrapped in a RuntimeException because the cluster-state applier path does not declare checked IOException; the original IOException is preserved as the cause.

Source

Thrown at modules/data-streams/src/main/java/org/elasticsearch/datastreams/action/TransportGetDataStreamsAction.java:308

                        state.metadata()
                    );
                    Settings templateSettings = MetadataIndexTemplateService.resolveSettings(
                        template,
                        state.metadata().componentTemplates()
                    );
                    final Settings settings = templateSettings.merge(dataStream.getSettings());
                    ilmPolicyName = settings.get(IndexMetadata.LIFECYCLE_NAME);
                    if (indexMode == null && state.metadata().templatesV2().get(indexTemplate) != null) {
                        try {
                            indexMode = resolveMode(
                                state,
                                indexSettingProviders,
                                dataStream,
                                settings,
                                dataStream.getEffectiveIndexTemplate(state.metadata())
                            );
                        } catch (IOException e) {
                            throw new RuntimeException("Failed to determine indexMode for data stream: " + dataStream.getName(), e);
                        }
                    }
                    indexTemplatePreferIlmValue = PREFER_ILM_SETTING.get(settings);
                } else {
                    LOGGER.warn(
                        "couldn't find any matching template for data stream [{}]. has it been restored (and possibly renamed)"
                            + "from a snapshot?",
                        dataStream.getName()
                    );
                }
            }

            ClusterStateHealth streamHealth = new ClusterStateHealth(
                state.cluster(),
                dataStream.getIndices().stream().map(Index::getName).toArray(String[]::new),
                state.projectId()
            );

View on GitHub (pinned to db6a809a66)

Solutions

1. Inspect the wrapped IOException cause for the underlying parse/merge failure.
2. Correct or recreate the offending composable index template referenced by the data stream.
3. If caused by version skew, ensure all nodes are on a compatible version and re-simulate the template with POST _index_template/_simulate_index.

try {
  DataStream resolved = resolveMode(state, providers, dataStream, settings, template);
} catch (IOException | RuntimeException e) {
  Throwable cause = e.getCause() != null ? e.getCause() : e;
  log.warn("failed to determine indexMode for data stream {}", dataStream.getName(), cause);
  // surface a clearer error to the caller; do not silently default the mode
  throw new IllegalStateException("cannot resolve index mode for " + dataStream.getName(), cause);
}

When it happens

Trigger: GET _data_stream during a state where the data stream's effective index template is present but its composable template definition fails to parse or its settings cannot be merged to compute a mode. Corrupted/invalid template metadata in the cluster state triggers it.

Common situations: Cluster state with a malformed or version-mismatched index template after upgrade/restore; concurrent template update leaving transient inconsistency; custom index_setting_provider throwing.

Related errors

• backing index [%s] in tsdb mode doesn't have the [%s] index
• Cannot add dynamic templates that define dimension fields on
• Expected at most one {} implementation, found: {}
• failed to parse value%s for setting [%s], must be lower than
• data streams {} not found

AI-assisted analysis of elastic/elasticsearch@db6a809a66 (2026-08-12). Data as JSON: /api/errors/0b1fa3e1374d63c9. Report an issue: GitHub.