Elasticsearch / OpenSearch, indexed, secured, sub-second.

Evaluates primary and replica shard distribution, detects skewed large shards, and diagnoses root causes for unassigned or red-state indices.

# Check shard distribution, size skew, and unassigned shards sorted by size
curl -s "localhost:9200/_cat/shards?v&s=store:desc" | head -n 25

# Explain why an unassigned shard cannot be allocated by the master node
curl -s "localhost:9200/_cluster/allocation/explain?pretty"

Monitors old-generation garbage collection pauses, heap usage ratios, and threadpool rejection counters to detect indexing backpressure.

# Inspect JVM heap pressure, GC pause accumulation, and indexing/search stats
curl -s "localhost:9200/_nodes/stats/jvm,indices/search,indexing?pretty" | jq '.nodes[] | {name, heap_used_percent: .jvm.mem.heap_used_percent, gc_old_ms: .jvm.gc.collectors.old.collection_time_in_millis}'

# Check write and search threadpool queues for 429 rejected executions
curl -s "localhost:9200/_cat/thread_pool/write,search?v&h=node_name,name,active,queue,rejected,completed"