[Meta] Migrations to OpenSearch

[setiah]

The purpose of this issue is track any gaps or issues users face in migrating their workloads to OpenSearch or within OpenSearch (for example, version upgrades). Since Migrations is a broad topic, this meta issue would be helpful in capturing and linking back all migration related pieces together at one place.

The scope of Migrations includes but is not limited to -

• Migration from previous Elasticsearch versions to any OpenSearch version
• Migration from ODFE to OpenSearch
• Migration from a lower OpenSearch version to higher OpenSearch version
• Migration of plugins
• Migration on any platform (RPM, Windows, Docker, etc.)
• Recommended tools/mechanisms available for migration.
• Areas of opportunities to build new tools/mechanisms for migrations
• Gaps in the documentation w.r.t. Migration.

This issue is open for feedback and discussions.

[setiah]

One area of improvement is lack of a good documentation that can serve as a migration guide. Created this issue for tracking opensearch-project/documentation-website#745

[setiah]

Some other areas called out by the community that lack migration support -

1. Migration of x-pack plugins to OpenSearch plugins. For instance, migrating x-pack Security to OpenSearch Security plugin, same for alerting and others.
2. Missing Spring Data integration [PROPOSAL] Introduce spring-data-opensearch to support OpenSearch integration spring-projects/spring-data-elasticsearch#1918

[reta]

Add flattened field type - #1018
Support for unsigned_long as same as in elastic search - #3538
Adding 'dense_vector' field type - #3659

[setiah]

Snapshotting plugin configurations for simple restore like data for easy migration of plugins - #3507

[brijos]

This is what we are tracking as migration blockers for language and ingestion clients....

Hadoop client - opensearch-project/opensearch-hadoop#134
Logstash 8 support - opensearch-project/logstash-output-opensearch#132
Logstash Filter plugin support - opensearch-project/opensearch-clients#4

[setiah]

Migration from x-pack flattened data types to OpenSearch https://forum.opensearch.org/t/migration-via-snapshot-restore-mapping-roadblocks/7906

[setiah]

Tagging opensearch-project/opensearch-ruby#50 here as ruby client is important for ruby users to migrate to OpenSearch.