Updating unchanged ILM policies is not idempotent.

[apollo13]

Elasticsearch version (bin/elasticsearch --version): docker.elastic.co/elasticsearch/elasticsearch:7.16.2-amd64

Plugins installed: Whatever the docker container ships

JVM version (java -version): Whatever the docker container ships

OS version (uname -a if on a Unix-like system): Whatever the docker container ships

Description of the problem including expected versus actual behavior:

Updating an ILM policy always increases the version of the stored policy. @DaveCTurner suggested to open an issue here. I did not check if other operations (updating index templates and mappings) are idempotent or not.

Steps to reproduce:

1. docker run --rm -it -p 9200:9200 -e "discovery.type=single-node" -e "logger.org.elasticsearch=DEBUG" docker.elastic.co/elasticsearch/elasticsearch:7.16.2-amd64
2. Execute:

curl -XPUT "http://localhost:9200/_ilm/policy/my_policy" -H 'Content-Type: application/json' -d'{    "policy" : {      "phases" : {        "warm" : {          "min_age" : "10d",          "actions" : {            "forcemerge" : {              "max_num_segments" : 1            }          }        },        "delete" : {          "min_age" : "30d",          "actions" : {            "delete" : {              "delete_searchable_snapshot" : true            }          }        }      }    }}'

multiple times
3. Check the ILM version: curl http://localhost:9200/_ilm/policy/my_policy
4. The returned version is greater than 1 even though nothing changed

Provide logs (if relevant):

{"type": "server", "timestamp": "2021-12-23T13:49:21,187Z", "level": "DEBUG", "component": "o.e.c.s.MasterService", "cluster.name": "docker-cluster", "node.name": "bf70a0fe0f7e", "message": "executing cluster state update for [put-lifecycle-my_policy]", "cluster.uuid": "aXsX_Ks1QpiwA-BiYs8kDQ", "node.id": "AgZJParzQPy5L6a5EMU0Lw"  }
{"type": "server", "timestamp": "2021-12-23T13:49:21,188Z", "level": "INFO", "component": "o.e.x.i.a.TransportPutLifecycleAction", "cluster.name": "docker-cluster", "node.name": "bf70a0fe0f7e", "message": "updating index lifecycle policy [my_policy]", "cluster.uuid": "aXsX_Ks1QpiwA-BiYs8kDQ", "node.id": "AgZJParzQPy5L6a5EMU0Lw"  }
{"type": "server", "timestamp": "2021-12-23T13:49:21,189Z", "level": "DEBUG", "component": "o.e.x.c.i.PhaseCacheManagement", "cluster.name": "docker-cluster", "node.name": "bf70a0fe0f7e", "message": "policy [my_policy] is unchanged and no phase definition refresh is needed", "cluster.uuid": "aXsX_Ks1QpiwA-BiYs8kDQ", "node.id": "AgZJParzQPy5L6a5EMU0Lw"  }
{"type": "server", "timestamp": "2021-12-23T13:49:21,189Z", "level": "DEBUG", "component": "o.e.c.s.MasterService", "cluster.name": "docker-cluster", "node.name": "bf70a0fe0f7e", "message": "took [1ms] to compute cluster state update for [put-lifecycle-my_policy]", "cluster.uuid": "aXsX_Ks1QpiwA-BiYs8kDQ", "node.id": "AgZJParzQPy5L6a5EMU0Lw"  }
{"type": "server", "timestamp": "2021-12-23T13:49:21,189Z", "level": "DEBUG", "component": "o.e.c.s.MasterService", "cluster.name": "docker-cluster", "node.name": "bf70a0fe0f7e", "message": "cluster state updated, version [65], source [put-lifecycle-my_policy]", "cluster.uuid": "aXsX_Ks1QpiwA-BiYs8kDQ", "node.id": "AgZJParzQPy5L6a5EMU0Lw"  }

[elasticmachine]

Pinging @elastic/es-data-management (Team:Data Management)