[BUG] Constant keyword field type not working - index created in a defect state

[securitym0nkey]

Describe the bug

When trying to create an index with a constant_keyword field the index is created but fails to initialize the shards. Leaving the index in a defect state.

The logs show an error like the following, giving the hint that the mandatory value attribute is missing, though it was specified when creating the index.

[2024-07-03T16:26:47,523][WARN ][o.o.c.r.a.AllocationService] [opensearch-nodes-0] failing shard [failed shard, shard [romcom_movies][0], node[ZT3MePnSSUCwmjmHl2GVPA], [P], recovery_source[new shard recovery], s[INITIALIZING], a[id=5Xd3-2t9TZSOd-04YVLWug], unassigned_info[[reason=ALLOCATION_FAILED], at[2024-07-03T16:26:47.412Z], failed_attempts[4], failed_nodes[[ZT3MePnSSUCwmjmHl2GVPA, regeJ4etSYqEWfZNO-Z4CA]], delayed=false, details[failed shard on node [regeJ4etSYqEWfZNO-Z4CA]: failed to update mapping for index, failure MapperParsingException[Failed to parse mapping [_doc]: Field [genre] is missing required parameter [value]]; nested: OpenSearchParseException[Field [genre] is missing required parameter [value]]; ], allocation_status[no_attempt]], message [failed to update mapping for index], failure [MapperParsingException[Failed to parse mapping [_doc]: Field [genre] is missing required parameter [value]]; nested: OpenSearchParseException[Field [genre] is missing required parameter [value]]; ], markAsStale [true]]

Related component

Indexing

To Reproduce

Just run the snippet from the documentation.

PUT romcom_movies
{
  "mappings" : {
    "properties" : {
      "genre" : {
        "type": "constant_keyword",
        "value" : "Romantic comedy"
      }
    }
  }
}

The request will take a long time and finally fail with a 400 error, but the index is created.

Note when running GET romcom_movies the value attribute is actually missing.

{
  "romcom_movies": {
    "aliases": {},
    "mappings": {
      "properties": {
        "genre": {
          "type": "constant_keyword"
        }
      }
    },
    "settings": {
      "index": {
        "replication": {
          "type": "DOCUMENT"
        },
        "number_of_shards": "1",
        "provided_name": "romcom_movies",
        "creation_date": "1720024006906",
        "number_of_replicas": "1",
        "uuid": "cHW2U7hQR3iZ8mtRQOo4_w",
        "version": {
          "created": "136367827"
        }
      }
    }
  }
}

Expected behavior

Index gets created and works like described in the documentation.

Additional Details

Plugins
default plugins

Host/Environment (please complete the following information):

• OS: container on k8s
• Version 2.15.0

[kkewwei]

@securitym0nkey, yes, it's a bug, i will pleasure to fix it, if you haven't do.

[kkewwei]

@securitym0nkey I have found the reason, the reason is we set the default value for the type incorrectly, so the value is not serialized in the cluster metadata.

[dblock]

Looks like it was introduced in #12285, cc: @hasnain2808 @msfroh.