Question about Kafka image requirements in Strimzi operator

[smazsta]

Hello,

I have a question regarding the Kafka images required by the Strimzi operator. As I understand, the operator typically relies on three different Kafka images (current, previous, and the one in rollout) to handle rolling updates and ensure zero downtime.

I experimented a bit and found that I can run the operator successfully by pointing all three image slots to the same Kafka version. I also tried using placeholder images (e.g., busybox) for two of the slots and only specifying the main Kafka image for the active one, and the operator still seemed to function as expected.

My question is, does using the same image for all three slots, or non-Kafka placeholder images for the intermediate slots, pose any risks beyond potential issues when upgrading to a newer operator version in the future? Specifically, could this affect Kafka-related functionality or features (e.g., rolling updates, configuration changes, or compatibility) in ways that aren’t immediately obvious?

Thanks in advance for clarifying.

[scholzj]

Well, as long as you don't use these Kafka versions, you will be obviously fine. If you try to use those Kafka versions, then you will likely not be fine:

• It will simply fail if you use busybox instead of a compatible Kafka image
• If you use Kafka image with different version it might fail as well, but likely in a much more tricky ways.

I'm not sure what exactly your motivation is to do this. But I think the best way is to configure the images to some non-existing container image. That way, if you use the given Kafka version by mistake, you get an image pull error, which will make it pretty obvious what the problem is.