Downgrade vs Rollback

OpenSearch
1

Is it possible to rollback a partial upgrade of a cluster? For example, if only 1 node has been upgraded, and the cluster still reports the old version.

When I attempt to do this, the rolled back node will not start and I see the following message in the logs:

java.lang.IllegalStateException: cannot downgrade a node from version [2.19.2] to version [2.18.0] at org.opensearch.env.NodeMetadata.upgradeToCurrentVersion(NodeMetadata.java:107)

My understanding is downgrades are not possible once the cluster is upgraded but is a rollback possible if the cluster has not fully upgraded yet?

Versions: OpenSearch v2.18.0 and v2.19.2

2

@smth As far as I’m aware, restoring snapshots of the previous version is the only way for rollback/downgrade.

Once the data node is upgraded, there is no mechanism to revert that process except snapshot.

What’s the reason for the rollback? Is there any problem with your upgrade?

3

Thanks for your reponse @pablo! I’m working on an operator and trying to understand the expected behaviour in this scenario. But it sounds like neither rollbacks nor downgrades are possible without restoring from a snapshot. Thank you for clarifying!