in_forward: enable skip_invalid_event by default

[Watson1978]

Which issue(s) this PR fixes:
Fixes #

What this PR does / why we need it:
This PR will enable skip_invalid_event in in_forward by default.

If broken data is received for any reason, it may cause the following error.

2025-06-12 18:27:30 +0900 [error]: unexpected error on reading data host="127.0.0.1" port=55970 error_class=TypeError error="can't convert String into an exact number"
  2025-06-12 18:27:30 +0900 [error]: <internal:timev>:325:in 'Time.at'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/formatter_stdout.rb:42:in 'Fluent::Plugin::StdoutFormatter#format'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/out_stdout.rb:67:in 'Fluent::Plugin::StdoutOutput#format'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/out_stdout.rb:60:in 'block in Fluent::Plugin::StdoutOutput#process'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/event.rb:259:in 'block in Fluent::MessagePackEventStream#each'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/event.rb:258:in 'Array#each'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/event.rb:258:in 'Enumerable#each_with_index'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/event.rb:258:in 'Fluent::MessagePackEventStream#each'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/out_stdout.rb:59:in 'Fluent::Plugin::StdoutOutput#process'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/output.rb:865:in 'emit_sync'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/event_router.rb:115:in 'Fluent::EventRouter#emit_stream'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/in_forward.rb:329:in 'Fluent::Plugin::ForwardInput#on_message'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/in_forward.rb:226:in 'block in Fluent::Plugin::ForwardInput#handle_connection'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/in_forward.rb:263:in 'block (3 levels) in Fluent::Plugin::ForwardInput#read_messages'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/in_forward.rb:262:in 'MessagePack::Unpacker#feed_each'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/in_forward.rb:262:in 'block (2 levels) in Fluent::Plugin::ForwardInput#read_messages'
  2025-06-12 18:27:30 +0900 [error]: /Users/watson/src/fluentd/lib/fluent/plugin/in_forward.rb:273:in 'block in Fluent::Plugin::ForwardInput#read_messages'
...

When enable skip_invalid_event, the broken data are just skipped.

2025-06-18 11:16:40 +0900 [info]: #0 fluentd worker is now running worker=0
2025-06-18 11:16:49 +0900 [warn]: #0 skip invalid event: host="127.0.0.1" tag="incoming" time=-17 record=nil
2025-06-18 11:16:49 +0900 [warn]: #0 skip invalid event: host="127.0.0.1" tag="incoming" time="\xBD\uFFFD\u0000hR \uFFFD:`uN\uFFFD\uFFFDmessage\uFFFD" record=nil
2025-06-18 11:16:49 +0900 [warn]: #0 skip invalid event: host="127.0.0.1" tag="incoming" time=50 record=nil
2025-06-18 11:16:49 +0900 [warn]: #0 skip invalid event: host="127.0.0.1" tag="incoming" time=97 record=nil
...

And, when require_ack_response was configured to true in out_forward,

1. in_forward causes error_class=TypeError error="can't convert String into an exact number" error by broken data.
2. in_forward can't sent the ack response by above error.
3. out_forward causes error_class=Fluent::Plugin::ForwardOutput::NoNodesAvailable error="no nodes are available" error because in_forward doesn't send the ack response.
4. out_forward will retry to send broken data.
5. back to 1.

in_forward and out_forward will repeat errors and retries indefinitely.

If skip_invalid_event was configured to true in in_forward,
in_forward doesn't cause the error by broken data,
in_forward and out_forward don't repeat errors and retries.

So, Fluentd will be more stable by enabled skip_invalid_event.

About performance degradation

It shows the processing time of in_forward when receiving 1 GB of data.

• with skip_invalid_event false
  • 15.178013304 sec
• with skip_invalid_event true
  • 15.859435514 sec

Even when skip_invalid_event was enabled, I think the performance degradation was minimal.

Docs Changes:
fluent/fluentd-docs-gitbook#587

Release Note:
Same as the title.

[daipom]

Thanks!