Monitor a Migration

Use _status for one source index and _list for an overview.

Status Endpoint

curl -s 'http://localhost:9200/_plugins/_aosc/my-index-v1/_status' | jq '.'

Example shape, truncated to one shard:

{
  "migration_id": "21b526c5-4794-4a55-9186-2020f702a731",
  "source_index": "my-index-v1",
  "target_index": "my-index-v2",
  "alias": "my-index",
  "phase": "COMPLETED",
  "shard_routing_mode": "SAME_SHARD",
  "options": {
    "convergence_threshold_per_shard": 1000,
    "max_convergence_rounds_per_shard": 1000
  },
  "cutover_context": {
    "source_doc_count": 689217412,
    "target_doc_count": 689217412,
    "doc_count_validation_passed": true,
    "alias_swap_succeeded": true,
    "cutover_start_millis": 1781030652331,
    "cutover_end_millis": 1781030665206
  },
  "shards": {
    "0": {
      "phase": "COMPLETED",
      "last_replayed_seq_no": 8453324,
      "target_seq_no": 8453324,
      "backfill_cutoff_seq_no": 8448260,
      "backfill": { "status": "COMPLETED", "documents_indexed": 1012245, "rounds": 2025 },
      "replay": { "status": "COMPLETED", "operations_applied": 415, "current_gap": 0 },
      "convergence": { "status": "COMPLETED", "operations_applied": 4649, "rounds": 3978, "current_gap": 0 },
      "catching_up": { "status": "COMPLETED", "operations_applied": 0, "current_gap": 0 }
    }
  }
}

On large shard counts, the full _status response can be several MB because every shard includes phase counters and transition history.

Fields to Watch

Field	Meaning
phase	Coordinator phase.
shard_routing_mode	Routing strategy selected for the migration.
cutover_context.*	Document-count validation and alias-swap timing after completion starts.
error_message	Coordinator-level failure message when present.
shards.*.phase	Per-shard worker phase.
shards.*.error	Shard-level failure message when present.
shards.*.last_replayed_seq_no and shards.*.target_seq_no	Replay checkpoint and target sequence number.
shards.*.backfill.documents_indexed	Backfill document counter.
shards.*.replay.operations_applied	Replay operation counter.
shards.*.convergence.current_gap	Current convergence gap.
shards.*.convergence.rounds	Number of convergence rounds.
shards.*.catching_up.operations_applied	Final catch-up operation counter.
shards.*.*.bulk_retries	Bulk write retry counters for the phase.

Useful Queries

Show coordinator phase:

curl -s 'http://localhost:9200/_plugins/_aosc/my-index-v1/_status' | jq '.phase'

Show non-terminal shards:

curl -s 'http://localhost:9200/_plugins/_aosc/my-index-v1/_status' \
  | jq '.shards | to_entries[] | select(.value.phase | IN("COMPLETED", "CANCELLED", "FAILED") | not)'

Show failed shards:

curl -s 'http://localhost:9200/_plugins/_aosc/my-index-v1/_status' \
  | jq '.shards | to_entries[] | select(.value.phase == "FAILING" or .value.phase == "FAILED")'

Summarize shard phases:

curl -s 'http://localhost:9200/_plugins/_aosc/my-index-v1/_status' \
  | jq '.shards | to_entries | group_by(.value.phase) | map({phase: .[0].value.phase, count: length})'

Compute the cutover-context duration after completion starts:

curl -s 'http://localhost:9200/_plugins/_aosc/my-index-v1/_status' \
  | jq '(.cutover_context.cutover_end_millis - .cutover_context.cutover_start_millis) / 1000'

List active migrations:

curl -s 'http://localhost:9200/_plugins/_aosc/_list?status=ACTIVE' | jq '.'

Status Source

Active migrations are served from the coordinator cache when available. Terminal or older migrations are read from .aosc-migrations.

If the status endpoint returns not found, check _list and cluster logs to determine whether the migration never started, has already been cleaned up, or the source index name is wrong.