Controlling the user cache
User credentials are cached in memory on each node to avoid connecting to a remote authentication service or hitting the disk for every incoming request. You can configure characteristics of the user cache with the cache.ttl, cache.max_users, and cache.hash_algo realm settings.
PKI realms do not cache user credentials but do cache the resolved user object to avoid unnecessarily needing to perform role mapping on each request.
The cached user credentials are hashed in memory. By default, the Elasticsearch security features use a salted sha-256 hash algorithm. You can use a different hashing algorithm by setting the cache.hash_algo realm settings. See User cache and password hash algorithms.
Evicting users from the cache
You can use the clear cache API to force the eviction of cached users . For example, the following request evicts all users from the ad1 realm:
$ curl -XPOST 'http://localhost:9200/_security/realm/ad1/_clear_cache'
To clear the cache for multiple realms, specify the realms as a comma-separated list:
$ curl -XPOST 'http://localhost:9200/_security/realm/ad1,ad2/_clear_cache'
You can also evict specific users:
$ curl -XPOST 'http://localhost:9200/_security/realm/ad1/_clear_cache?usernames=rdeniro,alpacino'
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https://www.elastic.co/guide/en/elasticsearch/reference/7.17/controlling-user-cache.html
