ES Indexing errors with this plugin about graylog-plugin-metrics-reporter

[TotalGriffLock]

Here's the dynamic template generated for this index (and therefore this plugin's messages because nothing else logs to that input)

$ curl -X GET "localhost:9200/_template/gelf-template?pretty=true"

{
  "gelf-template" : {
    "order" : -1,
    "index_patterns" : [
      "gelf_*"
    ],
    "settings" : {
      "index" : {
        "analysis" : {
          "analyzer" : {
            "analyzer_keyword" : {
              "filter" : "lowercase",
              "tokenizer" : "keyword"
            }
          }
        }
      }
    },
    "mappings" : {
      "_source" : {
        "enabled" : true
      },
      "dynamic_templates" : [
        {
          "internal_fields" : {
            "mapping" : {
              "type" : "keyword"
            },
            "match_mapping_type" : "string",
            "match" : "gl2_*"
          }
        },
        {
          "store_generic" : {
            "mapping" : {
              "type" : "keyword"
            },
            "match_mapping_type" : "string"
          }
        }
      ],
      "properties" : {
        "gl2_processing_timestamp" : {
          "format" : "uuuu-MM-dd HH:mm:ss.SSS",
          "type" : "date"
        },
        "gl2_accounted_message_size" : {
          "type" : "long"
        },
        "gl2_receive_timestamp" : {
          "format" : "uuuu-MM-dd HH:mm:ss.SSS",
          "type" : "date"
        },
        "full_message" : {
          "fielddata" : false,
          "analyzer" : "standard",
          "type" : "text"
        },
        "streams" : {
          "type" : "keyword"
        },
        "source" : {
          "fielddata" : true,
          "analyzer" : "analyzer_keyword",
          "type" : "text"
        },
        "message" : {
          "fielddata" : false,
          "analyzer" : "standard",
          "type" : "text"
        },
        "timestamp" : {
          "format" : "uuuu-MM-dd HH:mm:ss.SSS",
          "type" : "date"
        }
      }
    },
    "aliases" : { }
  }
}

The only field which is a [long] is gl2_accounted_message_size. So is this plugin causing that field to sometimes contain the timestamp or a null value?

[TotalGriffLock]

I have resolved this myself, via https://community.graylog.org/t/graylog-metrics-plugin-feeding-data-via-gelf-to-graylog-causing-parsing-errors/16356/3

Most of the values for metrics are numbers so Graylog/ES correctly decide to store the "value" field as a [long]. However there are 2 metrics (at the time of writing):
org.graylog2.journal.oldest-segment
jvm.threads.deadlocks
where the value is either a string (timestamp) or a collection/array. Obviously this data will not go in a field with the type of long. The graylog community URL above provides a solution but only for 1 specific metric. I've put the GELF metrics input through a pipeline with the following rule, which has resolved the errors for me and should work as new metrics are added which are not numeric:

Rule "Cleanup: Non-numeric metrics value field"
when
has_field("value") AND
not is_long("value")
then
rename_field(
old_field: "value",
new_field: "value_string"
);
end

[TotalGriffLock]

That didn't appear to be working either, but this does. Can't spend any more time on it right now, but if anyone else is having the same problem this will fix it.

Rule "Cleanup: Non-numeric metrics value field"
when
has_field("name") AND
has_field("value") AND
(to_string($message.name) == "org.graylog2.journal.oldest-segment" OR
to_string($message.name) == "jvm.threads.deadlocks")
then
let value_string = to_string($message.value);
set_field ("value_string",value_string);
remove_field("value");
end