Add add_tag_prefix parameter to out_forward (like in_forward has)

[Lukas-Ldc]

Is your feature request related to a problem? Please describe.

When using out_forward to send logs to multiple different destinations, there's no way to simply add a tag prefix for a specific destination. This is problematic when the remote FluentD is not under your control, so you can't use add_tag_prefix on their in_forward.

Describe the solution you'd like

Could you please implement the add_tag_prefix parameter to out_forward, similar to what already exists in in_forward. This would be a simple, performant solution that keeps the FluentD configuration clean and straightforward.

Describe alternatives you've considered

rewrite_tag_filter - I tried using this plugin but encountered issues and couldn't get it to work properly (don't remember exactly, but probably because events were re-routed through the entire pipeline). I think it also has performance overhead.

Additional context

No response

[Watson1978]

Isn't the pattern of using the out_copy and out_forward plugins sufficient in this use case?

[Lukas-Ldc]

I may be missing something, but I'm not sure how out_copy + out_forward can modify the tag before sending. Could you provide a quick example of how this would work?

[Watson1978]

If you want to send the same message to multiple destinations, you can configure it as follows:

# input
<source>
  @type sample
  tag test
</source>

# output
<match test>
  @type copy
  # destination A
  <store>
    @type forward
    <server>
      host 127.0.0.1
      port 24224
    </server>
  </store>

  # destination B
  <store>
    @type forward
    <server>
      host 192.168.10.199
      port 24224
    </server>
  </store>
</match>

Please refer to https://docs.fluentd.org/output/copy for details of out_copy plugin.

[Lukas-Ldc]

Thank you for the example. However, this sends the same tag to both destinations.
My need is to send different tags to each destination (e.g., test to destination A and prefix.test to destination B).

[Watson1978]

You can use rewrite_tag_filter plugin to modify the tag.

<match test>
  @type copy
  # destination A
  <store>
    @type forward
    <server>
      host 127.0.0.1
      port 24224
    </server>
  </store>

  # destination B
  <store>
    @type rewrite_tag_filter
    <rule>
      key message
      pattern .*
      tag test.destB
    </rule>
  </store>
</match>

<match test.destB>
  @type forward
  <server>
    host 192.168.10.102
    port 24224
  </server>
</match>