Filebeat failed to publish events: temporary bulk send failure

[cdalexndr]

Filebeat 7.14.1 is stuck in a log loop with failed to publish events: temporary bulk send failure.

Turning debug log, it shows:

filebeat  | 2021-11-07T15:57:49.938Z    INFO    [publisher_pipeline_output]     pipeline/output.go:151  Connection to backoff(elasticsearch(http://elasticsearch:9200)) established
filebeat  | 2021-11-07T15:57:49.941Z    DEBUG   [elasticsearch] elasticsearch/client.go:227     PublishEvents: 1 events have been published to elasticsearch in 3.1342ms.
filebeat  | 2021-11-07T15:57:49.941Z    DEBUG   [elasticsearch] elasticsearch/client.go:411     Bulk item insert failed (i=0, status=500): {"type":"string_index_out_of_bounds_exception","reason":"String index out of range: 0"}
filebeat  | 2021-11-07T15:57:49.941Z    INFO    [publisher]     pipeline/retry.go:219   retryer: send unwait signal to consumer
filebeat  | 2021-11-07T15:57:49.941Z    INFO    [publisher]     pipeline/retry.go:223     done
filebeat  | 2021-11-07T15:57:51.776Z    ERROR   [publisher_pipeline_output]     pipeline/output.go:180  failed to publish events: temporary bulk send failure

This error is so criptic with missing information that I don't know how to get more information...
What String caused error, doing what???
I've searched Elasticsearch logs for string_index_out_of_bounds_exception but didn't found anything.

My filebeat.yml:

output.elasticsearch:
  hosts: ["http://elasticsearch:9200"]
  index: "log-%{[docker][container][labels][app]}"
  pipeline: pipeline_logs
  ilm.enabled: false

logging.level: debug

queue.mem:
  events: 1024
  flush.min_events: 256
  flush.timeout: 1s

setup.ilm.enabled: false
setup.template.enabled: false
setup.kibana.host: http://kibana:5601

filebeat.autodiscover:
  providers:
    - type: docker
      hints.enabled: true
      templates:
        - condition:
            contains:
              docker.container.image: swag
          config:
            - module: nginx
              access:
                enabled: true
                var.paths: [ "/config/log/nginx/access.log*" ]
              error:
                enabled: true
                var.paths: [ "/config/log/nginx/error.log*" ]

My pipeline_logs has an on_failure fallback processor, but it seems the problem is somewhere else:

{
  "description": "Log dispatcher ingest pipeline",
  "processors": [
    {
      "set": {
        "field": "app_name",
        "value": "{{docker.container.labels.app}}",
        "ignore_empty_value" : true
      }
    },
    {
      "pipeline": {
        "if": "ctx.app_name == 'autoheal'",
        "name": "pipeline_autoheal"
      }
    },
    {
      "pipeline": {
        "if": "ctx.app_name == 'web'",
        "name": "pipeline_web"
      }
    },
    {
      "pipeline": {
        "if": "ctx.app_name == null",
        "name": "pipeline_fallback"
      }
    },
    {
      "uppercase": {
        "field": "log.level",
        "if": "ctx.log?.level != null"
      }
    },
    {
      "set": {
        "field": "level",
        "value": "{{log.level}}",
        "if": "ctx.log?.level != null"
      }
    }
  ],
  "on_failure": [
    {
      "set": {
        "description": "Record error information",
        "field": "error",
        "value": "Processor '{{ _ingest.on_failure_processor_type }}' with tag '{{ _ingest.on_failure_processor_tag }}' in pipeline '{{ _ingest.on_failure_pipeline }}' failed with message: {{ _ingest.on_failure_message }}"
      }
    }
  ]
}

I've done some pipeline tests in Kibana and it seems to be working fine.

[cdalexndr]

I've narrowed it down to a container (mariadb:latest) that when running, causes filebeat to stop working.

But I've run all my mariadb container log lines through my pipeline (Kibana test pipeline) and none failed...

My mariadb container has no labels for filebeat configuration.