chore: Accept 204 from FluentD responses

[cgetzen]

Problem

Many orgs already have logging infrastructure in place, but do not use FluentD. In this case, Teleport Audit Event Logging requires teams to install and manage FluentD in addition to existing infra.

Solution

This relaxes the status code validation for FluentD responses, in order to allow other log aggregators to accept the event handlers requests.

The changes in this PR allow Grafana Alloy to be used as a replacement for FluentD, by using the loki.sources.api component and configuring the Teleport event handler to point url and session-url to Alloy's /loki/api/v1/raw endpoint.

This change should accommodate any Log Collectors that support raw JSON and emit 200 or 204 status codes.

Without these changes in place, logs get duplicated in our logging infra:

Stack Trace:
        github.com/gravitational/teleport/integrations/event-handler/fluentd_client.go:134 main.(*FluentdClient).Send
        github.com/gravitational/teleport/integrations/event-handler/app.go:116 main.(*App).SendEvent
        github.com/gravitational/teleport/integrations/event-handler/events_job.go:313 main.(*EventsJob).sendEvent
        github.com/gravitational/teleport/integrations/event-handler/events_job.go:288 main.(*EventsJob).handleEvent
        github.com/gravitational/teleport/integrations/event-handler/events_job.go:282 main.(*EventsJob).handleEventV2
        github.com/gravitational/teleport@v0.0.0/lib/events/export/date_exporter.go:599 github.com/gravitational/teleport/lib/events/export.(*DateExporter).exportEvents
        github.com/gravitational/teleport@v0.0.0/lib/events/export/date_exporter.go:456 github.com/gravitational/teleport/lib/events/export.(*DateExporter).processChunk
        github.com/gravitational/teleport@v0.0.0/lib/events/export/date_exporter.go:433 github.com/gravitational/teleport/lib/events/export.(*DateExporter).startProcessingChunk.func2
        runtime/asm_amd64.s:1700 runtime.goexit
User Message: Failed to send event to fluentd (HTTP 204)] attempts:5 event-handler/app.go:133

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[programmerq]

From the docs for the Fluentd HTTP input plugin:

use_204_response bool false
Respond status code with 204. This option will be deprecated at v2 because fluentd v2 will respond 204 as default.

It seems future versions of Fluentd will also respond with a 204, so we should definitely allow at least 200 and 204. I'll let our devs comment on whether we want to accept all 2XX response codes or not.

[cgetzen]

@programmerq nice find. This has been adjusted to only accept 200 and 204.

[programmerq]

LGTM

[cgetzen]

recheck

[cgetzen]

You can retrigger this bot by commenting recheck in this Pull Request. Posted by the CLA Assistant Lite bot

I am not sure if this, or the "CLA Assistant" CI check, is working correctly.

[bernardjkim]

Hey, change looks good to me. I'll go ahead and approve the GHA workflows and add the PR to the merge queue. I'll also follow up with the backport PRs.

Edit: Seems like our CI pipeline is having some issues with external contributions. I've created a buddy PR with your commits here: #57581.

[hugoShaka]

Merged in: #57581