ES is upgraded from version 6.3.2 to 6.8.22 in a rolling manner. After the upgrade, the cluster status is abnormal. How to roll back to 6.3.2?

Currently I am working on the ES rolling upgrade plan. The official manual lists the rolling upgrade steps, but there is no rollback step. After the ES rolling upgrade, the cluster status is abnormal or the application wants to roll back to 6.3.2. How to do it? Rollback from ES version 6.8.22 to 6.3.2

Elasticsearch does not support rollbacks, so the only way to get back to 6.3.2 would be to restore a snapshot taken with that version prior to the upgrade into a downgraded 6.3.2 cluster.

It is probably better to fix the issue you are having. What is the issue with the cluster status? What is in the Elasticsearch logs?

Currently, I am working on a rolling upgrade plan for ES, from version 6.3.2 to 6.8.22. In order to prevent uncontrollable problems during the upgrade and cannot be solved in a short time, I hope to have a cluster upgrade rollback plan to deal with

As Christian mentioned, the only plan is to take a snapshot and restore that.

Thanks for the reply, I have a question about rolling upgrades, the part marked in the following text, is it understood that it is not allowed to accept multiple ES versions for a long time during the upgrade? However, the actual rolling upgrade requires a gradual upgrade of nodes one by one, and needs to wait for the node status to recover and the cluster status to recover to green, which may take a long time. During this period, two versions of ES must exist in the cluster at the same time.

Rolling upgrades
A rolling upgrade allows an Elasticsearch cluster to be upgraded one node at a time so upgrading does not interrupt service. Running multiple versions of Elasticsearch in the same cluster beyond the duration of an upgrade is not supported, as shards cannot be replicated from upgraded nodes to nodes running the older version.

Yeah, as in days/weeks. A few hours is fine.

So is it safer to roll the upgrade in a few hours? The largest amount of ES cluster data in our production environment exceeds 20TB, so I am worried that the rolling upgrade will take a long time. Is there a precise time requirement for the rolling upgrade to complete?

There's no hard limits here, but hours is ok.

ok thanks for your reply

ES rolling upgrade, upgrade from version 6.3.2 to 6.8.22 and version 7.x to 7.16.2, does the client application need to make any changes? What preparations and inspections need to be done before upgrading?

Most likely. You will need to read the breaking changes for the client and do testing