Indices with no write index defined should be logged at info/warn level

[Battleroid]

I was hoping in the future if it is possible for these types of errors to be reported at the INFO/WARN level instead of DEBUG. Right now occasionally we'll get a slow build up of events that have no such write index for their given alias. Unfortunately to even discover if this is the cause, we need to flip debug level logging on for the instances and sift through a ton of empty filler to find a single message that helps us resolve the problem.

Contrary to the level in the message, we don't actually see these either until we set the logging level to debug.

• Version: 7.x
• Sample Data:

   {
    "level": "ERROR",
    "loggerName": "logstash.outputs.elasticsearch",
    "timeMillis": 1618239497168,
    "thread": "[main]>worker10",
    "logEvent": {
      "message": "Encountered a retryable error. Will Retry with exponential backoff ",
      "code": 400,
      "url": "https://sample-host.com:9200/_bulk",
      "body": "{\"error\":{\"root_cause\":[{\"type\":\"illegal_argument_exception\",\"reason\":\"no write index is defined for alias [sample-index]. The write index may be explicitly disabled using is_write_index=false or the alias points to multiple indices without one being designated as a write index\"}],\"type\":\"illegal_argument_exception\",\"reason\":\"no write index is defined for alias [sample-index]. The write index may be explicitly disabled using is_write_index=false or the alias points to multiple indices without one being designated as a write index\"},\"status\":400}"
    }
  }
  

• Steps to Reproduce:
  • Remove is_write_index: true from any given alias with it set or that is ILM managed.