[DOC] Document when to upgrade OpenSearch Dashboards node on a rolling upgrade

[cwperks]

What do you want to do?

The rolling upgrade documentation does not clearly mention when to upgrade the OpenSearch Dashboards node during the process. I'm not sure what is recommended, but I went through the code and will highlight a few areas.

There is a notion of compatibility between OS nodes and OSD and you can find details in the following fn https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/core/ser[…]check/opensearch_opensearch_dashboards_version_compatability.ts:

1. Reject mismatching major versions
2. OSD minor version cannot be ahead of OS version

Assuming the nodes meet compatibility requirements, then OSD will collect a list of warningNodes and log out the nodes where the OS version and OSD version do not match. https://github.com/opensearch-project/OpenSearch-Dashboards/blob/main/src/core/server/opensearch/version_check/ensure_opensearch_version.ts#L189C3-L196

At first glance it looks like for a patch release it can be at any time during the rolling upgrade, but it may different for minor and major upgrades and have to occur after every node has been upgraded.

• [X] Request a change to existing documentation
• [ ] Add new documentation
• [ ] Report a technical problem with the documentation
• [ ] Other

[hdhalter]

Hi Jeff, is this something you can take a look at? Thanks.