Added support for feature flags in opensearch.yml (#4959)

This change introduces a static store "settings"
in FeatureFlags.java file to enable isEnabled method to
fetch flag settings defined in opensearch.yml.

Signed-off-by: Nagaraj Tantri <nagarajtantri@gmail.com>

(cherry picked from commit 241bd42)

CHANGELOG.md

@@ -3,6 +3,20 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ## [Unreleased]
 ### Added
+- Add support of default replica count cluster setting ([#5610](https://github.com/opensearch-project/OpenSearch/pull/5610))
+- Apply reproducible builds configuration for OpenSearch plugins through gradle plugin ([#4746](https://github.com/opensearch-project/OpenSearch/pull/4746))
+- Prevent deletion of snapshots that are backing searchable snapshot indexes ([#5069](https://github.com/opensearch-project/OpenSearch/pull/5069))
+- Update to Gradle 7.6 ([#5382](https://github.com/opensearch-project/OpenSearch/pull/5382))
+- Reject bulk requests with invalid actions ([#5299](https://github.com/opensearch-project/OpenSearch/issues/5299))
+- Add max_shard_size parameter for shrink API ([#5229](https://github.com/opensearch-project/OpenSearch/pull/5229))
+- Added jackson dependency to server ([#5366](https://github.com/opensearch-project/OpenSearch/pull/5366))
+- Adding support to register settings dynamically ([#5495](https://github.com/opensearch-project/OpenSearch/pull/5495))
+- Adding auto release workflow ([#5582](https://github.com/opensearch-project/OpenSearch/pull/5582))
+- Added experimental support for extensions ([#5347](https://github.com/opensearch-project/OpenSearch/pull/5347)), ([#5518](https://github.com/opensearch-project/OpenSearch/pull/5518)), ([#5597](https://github.com/opensearch-project/OpenSearch/pull/5597)), ([#5615](https://github.com/opensearch-project/OpenSearch/pull/5615)))
+- Add CI bundle pattern to distribution download ([#5348](https://github.com/opensearch-project/OpenSearch/pull/5348))
+- Added @gbbafna as an OpenSearch maintainer ([#5668](https://github.com/opensearch-project/OpenSearch/pull/5668))
+- Experimental support for extended backward compatiblity in searchable snapshots ([#5429](https://github.com/opensearch-project/OpenSearch/pull/5429))
+- Add feature flag for extensions ([#5211](https://github.com/opensearch-project/OpenSearch/pull/5211))
 - Add support for s390x architecture ([#4001](https://github.com/opensearch-project/OpenSearch/pull/4001))
 - Github workflow for changelog verification ([#4085](https://github.com/opensearch-project/OpenSearch/pull/4085))
 - Point in time rest layer changes for create and delete PIT API ([#4064](https://github.com/opensearch-project/OpenSearch/pull/4064))
@@ -11,12 +25,12 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 - Added @dreamer-89 as an Opensearch maintainer ([#4342](https://github.com/opensearch-project/OpenSearch/pull/4342))
 - Added release notes for 1.3.5 ([#4343](https://github.com/opensearch-project/OpenSearch/pull/4343))
 - Added release notes for 2.2.1 ([#4344](https://github.com/opensearch-project/OpenSearch/pull/4344))
-- Label configuration for dependabot PRs ([#4348](https://github.com/opensearch-project/OpenSearch/pull/4348))
-- Support for HTTP/2 (server-side) ([#3847](https://github.com/opensearch-project/OpenSearch/pull/3847))
 - BWC version 2.2.2 ([#4383](https://github.com/opensearch-project/OpenSearch/pull/4383))
 - Support for labels on version bump PRs, skip label support for changelog verifier ([#4391](https://github.com/opensearch-project/OpenSearch/pull/4391))
 - Add a new node role 'search' which is dedicated to provide search capability ([#4689](https://github.com/opensearch-project/OpenSearch/pull/4689))
 - Introduce experimental searchable snapshot API ([#4680](https://github.com/opensearch-project/OpenSearch/pull/4680))
+- Added support for feature flags in opensearch.yml ([#4959](https://github.com/opensearch-project/OpenSearch/pull/4959))
+
 ### Dependencies
 - Bumps `com.diffplug.spotless` from 6.9.1 to 6.10.0
 - Bumps `xmlbeans` from 5.1.0 to 5.1.1

distribution/src/config/opensearch.yml

@@ -86,3 +86,26 @@ ${path.logs}
 # Require explicit names when deleting indices:
 #
 #action.destructive_requires_name: true
+#
+# ---------------------------------- Experimental Features -----------------------------------
+#
+# Gates the visibility of the index setting that allows changing of replication type.
+# Once the feature is ready for production release, this feature flag can be removed.
+#
+#opensearch.experimental.feature.replication_type.enabled: false
+#
+#
+# Gates the visibility of the index setting that allows persisting data to remote store along with local disk.
+# Once the feature is ready for production release, this feature flag can be removed.
+#
+#opensearch.experimental.feature.remote_store.enabled: false
+#
+#
+# Gates the functionality of a new parameter to the snapshot restore API
+# that allows for creation of a new index type that searches a snapshot
+# directly in a remote repository without restoring all index data to disk
+# ahead of time.
+#
+#opensearch.experimental.feature.searchable_snapshot.enabled: false
+#
+#