Problem:

The ImageDigestMirrorSet API (IDMS) currently requires nodes to drain when any entries are REMOVED from the IDMS or related ImageTagMirrorSet (ITMS). This decision was made to make it obvious to the administrator that a future image pull failure could be associated with the change to the IDMS/ITMS.

When customers use fine-grained IDMS or ITMS policies which result in hundreds or thousands of images, it makes it difficult to prevent node drains when images are no longer needed.

A prominent example of this is oc-mirror with --max-components flag set and pruning enabled (the default).

Proposal:

Add a value to the IDMS and ITMS to allow the user to opt-out of the node drain.
.spec.drainNodeOnRemoval :

• If true (default), drain the nodes.
• If false, apply removals to the nodes without draining.

This value applies to the values in the current IDMS/ITMS file. It also applies if the IDMS/ITMS is deleted in its entirety.

Alternatives:

Cluster-Global setting

Although this may be easier to implement, it's not as desirable since the customer may want to conditionally enable node drains for different use cases (flexibility).