Add gelf output plugin to fluentbit

[alexandrevilain]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #881

Does this PR introduced a user-facing change?

Add gelf output plugin to fluentbit

Additional documentation, usage docs, etc.:

[wenchajun]

Is the corresponding match field missing?

[alexandrevilain]

Hi @wenchajun ! Thanks for the review.

Is the corresponding match field missing?

I don't think it's missing because it's handled by this part of the code: https://github.com/fluent/fluent-operator/blob/master/apis/fluentbit/v1alpha2/clusteroutput_types.go#L153

If I create the following manifest:

apiVersion: fluentbit.fluent.io/v1alpha2
kind: ClusterOutput
metadata:
  name: test
  labels:
    fluentbit.fluent.io/enabled: "true"
    fluentbit.fluent.io/mode: "fluentbit-only"
spec:
  matchRegex: "*"
  gelf:
    host: 127.0.0.1
    port: 12202
    mode: tls
    tls:
      verify: true

The generated configuration looks like:

[Output]
    Name    gelf
    Match_Regex    *
    Host    gra1.logs.ovh.com
    Port    12202
    Mode    tls
    tls    On
    tls.verify    true

Here it uses matchRegex but it's the same as for match.

I think that it's an error on the GELF output documentation as the "Match" field is part of every output plugin.
But maybe I'm wrong ?

[wenchajun]

The match field here is generic, it is used to match the tag of the log channel in fluentbit. but I read the official docs of fluentbit that the match field in the plugin is exclusive, so was wondering why it is not added.
Other plugins also have this generic match field.

[benjaminhuo]

@patrick-stephens @wanjunlei what do you think?

[patrick-stephens]

@patrick-stephens @wanjunlei what do you think?

Not sure what you're querying here - all filter+output plugins support match and match_regex.
I think the docs have just included the field explicitly.

[benjaminhuo]

@patrick-stephens @wanjunlei what do you think?

Not sure what you're querying here - all filter+output plugins support match and match_regex. I think the docs have just included the field explicitly.

Agree, Match & MatchRegex are common attributes of output plugins:
https://docs.fluentbit.io/manual/administration/configuring-fluent-bit/classic-mode/configuration-file#config_output
https://github.com/fluent/fluent-operator/blob/master/apis/fluentbit/v1alpha2/clusteroutput_types.go#L39