chore: [receiver/kafka] docs add example of connecting to kafka with sasl +tls

[povilasv]

Description:

Adding an example on how to connect to kafka that needs both tls and sasl config.

Link to tracking Issue: <Issue number if applicable> https://github.com/open-telemetry/opentelemetry-collector-contrib/issues/31931

Testing: <Describe what testing was performed and which tests were added.>

Documentation: <Describe the documentation added.>

[evan-bradley]

@povilasv @MovieStoreGuy What do you think about this? I would like to stay consistent with the OTLP receiver, which does:

receivers:
  otlp:
    protocols:
      grpc:

So we could just have it such that setting tls enables it. But we could also have a tls_enabled key, or try to put an enabled field in the tls section.

[povilasv]

@evan-bradley updated PR based on comments.

I've tried using:

  kafka:
    topic: meh
    brokers: localhost:9092
    auth:
      tls:

And it' seems that it renders tls section to nil and doesn't enable TLS.

So for now the only way is to set some field under auth :thinking:

[evan-bradley]

Sorry, I lost track of this.

And it' seems that it renders tls section to nil and doesn't enable TLS.

My bad, I should have been a bit clearer: I think we can update the code to work more like the OTLP receiver to allow merely setting the tls key to mean "enable TLS" by creating a default config, then setting it to nil if the user doesn't specify the key. Here's how the OTLP receiver does each:

1. Creating a default config: https://github.com/open-telemetry/opentelemetry-collector/blob/main/receiver/otlpreceiver/factory.go#L41
2. The default config is kept if the user sets the key, otherwise set to nil and disabled if they do not: https://github.com/open-telemetry/opentelemetry-collector/blob/main/receiver/otlpreceiver/config.go#L68

[MovieStoreGuy]

@povilasv @MovieStoreGuy What do you think about this? I would like to stay consistent with the OTLP receiver, which does:

receivers:
  otlp:
    protocols:
      grpc:

So we could just have it such that setting tls enables it. But we could also have a tls_enabled key, or try to put an enabled field in the tls section.

The config needs some love since it is somewhat of a sprawling mess as a side affect of how Kafka library exposes its configuration. I agree it needs some love, but I don't want to do a bunch of subtle changes that makes it hard to understand what changed.

Adding an example as an interim solution is acceptable until we can plan this out.

[povilasv]

The config needs some love since it is somewhat of a sprawling mess as a side affect of how Kafka library exposes its configuration. I agree it needs some love, but I don't want to do a bunch of subtle changes that makes it hard to understand what changed.

Adding an example as an interim solution is acceptable until we can plan this out.

I agree, I tried implementing it, but it's a bit hard. I think we should add the doc, so that users don't spend time debugging this and then later as a separate issue to figure out how to refactor this