docs(connect): clarifies image/version config for kafka connect

[PaulRMellor]

Documentation

Updates docs on using custom image for Kafka Connect to explain that a Kafka version should be specified.
Also refreshes content on image config for Kafka components to make it easier to scan

Checklist

Please go through this checklist and make sure all applicable tasks have been done

• Write tests
• Make sure all tests pass
• Update documentation
• Check RBAC rights for Kubernetes / OpenShift roles
• Try your changes from Pod inside your Kubernetes and OpenShift cluster, not just locally
• Reference relevant issue(s) and close them after merging
• Update CHANGELOG.md
• Supply screenshots for visual changes, such as Grafana dashboards

[scholzj]

I left some nits. I also wonder, if we have the upgrades covered here, because they are pretty tricky with the custom images. Beause you basically need to update the imahge field at the same point when the upgrade is happpening which is not possible. So the user likely needs to:

• Pause the reconciliation
• Upgrade the operator
• Upgrade the .spec.image
• Unpause the reconciliation

[scholzj]

This table is fine, but I'm not sure it captures the main issue which is What is the right configuration. The version field specifies two things:

• What image will be used if not set in the custom resoruce directly
• What is the expected Kafka version, which defines how the operator will manage the operand

As a result, some of these settings are possibly both valid and invalid.

---

Maybe we need to add some second table showing some valid and invalid configurations as examples? E.g.

• Imagine operator which supports Kafka 4.0.0, 4.0.1 and 4.1.0
• The configuration without custom image and verison is valid
• The configuration with custom image based on Kafka 4.0.0 with version set to 4.0.0 is valid
• The configuration with custom image based on Kafka 4.0.0 without version set is invalid because version defaults to 4.1.0 in this case
• etc.

[PaulRMellor]

Thanks. I've added a table with some examples where the config mismatches produce invalid results.

[scholzj]

IF we want to include this, we should have a warning that this would possibly impact other Connect clusters as well. In general, I do not expect STRIMZI_KAFKA_CONNECT_IMAGES to be used for manually build custom images as it does not make much sense

[PaulRMellor]

Okay. I've changed so the spec.image is shown in the step. The intro mentions this but also mentions what happens if the env var is updated instead.

[PaulRMellor]

I left some nits. I also wonder, if we have the upgrades covered here, because they are pretty tricky with the custom images. Beause you basically need to update the imahge field at the same point when the upgrade is happpening which is not possible. So the user likely needs to:

• Pause the reconciliation
• Upgrade the operator
• Upgrade the .spec.image
• Unpause the reconciliation

Great feedback, thanks.
I've added a section on upgrade.
I've assumed we're concerned with changes to Kafka versions here, rather than guidance on refreshing the image without the Kafka version changing.

[scholzj]

One more comment. But LGTM otherwise. Thanks for incorporating the changes.

[im-konge]

Thanks Paul :)