We want to make reindex resilient to node restarts and failures, such that reindex can continue to run across such events.

There are two primary problems to solve:

• Data node resiliency. Reindex relies on scroll queries which are not resilient.
• Coordinator node resiliency. Reindex runs on the host receiving the request and cannot survive if that node dies or is restarted.

Search resiliency

• Search ordered by seq_no and handle query failures by retrying from last seq_no (inclusive)
• Support reindex from remote when source version above 6.6+
• Add support for alternative numeric ordering attribute, particularly useful for remote index against pre-6.5 source.
• Back-off strategy on repeated failures
• Verify overhead of seq_no ordering

Coordinator node resiliency:

• POC to clarify this subject more (Make reindexing managed by a persistent task #43382)
• Decide on start reindex job action name
  • indices:data/write/start_reindex
  • indices:admin/reindex/start_reindex
  • cluster:admin/reindex/start_reindex
  • indices:data/reindex/start_reindex
• Decide on persistent reindex task name
• Evaluate how we want to do timeouts for waiting on initial task creation or reindex task completion
• Refactor common parts from data frames and roll-up
• Add reindex persistent task and remove it when done (Make reindexing managed by a persistent task #43382)
• Allocation of reindex persistent task (Make reindexing managed by a persistent task #43382)
• Store progress information periodically into .tasks index
• Resume from existing progress information when allocated to new node
• Make updates to persistent tasks resilient against master failovers
• Support async durability on destination, ensuring data in checkpoint is fsync'ed into destination

Slicing:

• Investigate having multiple in flight search and bulk requests as an alternative

Benchmarking:

• Compare rally original indexing to reindex
• Overhead of scripting and ingest pipelines

Misc:

• Handle write failures by retrying when appropriate
• Refined error handling, filter out known/retryable errors
• HLRC support for new persistent task id.
• Examine if transport client in 7.x can call resilient reindex (workaround).
• Add serialization tests for get reindex request

Docs

• Clarify how to use resilient reindex in reference docs (conflict handling, parameters)