Add Elasticsearch cluster maintenance documentation

[sarayourfriend]

Fixes

Related to #2744 which identified a missed step in the ES cluster upgrade process.

Description

I realised there was not a single place where ES cluster maintenance was comprehensively documented. This document includes everything I know about our ES cluster, including how to make configuration changes.

Docs preview: https://docs.openverse.org/_preview/3032/meta/maintenance/elasticsearch_cluster.html

Testing Instructions

Read the new document and identify any areas that need clarification. Remember the audience is the Openverse maintainers with infrastructure access, so any of the @WordPress/openverse-maintainers with the responsibility for infrastructure maintenance should be able to understand and employ this document.

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
• My pull request targets the default branch of the repository (main) or a parent feature branch.
• My commit messages follow best practices.
• My code follows the established code style of the repository.
• [N/A] I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible errors.
• [N/A] I ran the DAG documentation generator (if applicable).

Developer Certificate of Origin

Developer Certificate of Origin

Developer Certificate of Origin
Version 1.1

Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
1 Letterman Drive
Suite D4700
San Francisco, CA, 94129

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.


Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.

[github-actions]

Full-stack documentation: https://docs.openverse.org/_preview/3032

Please note that GitHub pages takes a little time to deploy newly pushed code, if the links above don't work or you see old versions, wait 5 minutes and try again.

You can check the GitHub pages deployment action list to see the current status of the deployments.

Changed files 🔄:

• https://docs.openverse.org/_preview/3032/meta/index.html

[krysal]

Thank you for documenting all the learnings from the ES update. This doc is excellent 💯

[krysal]

I wonder how restoring a backup between versions, if possible, compares in cost and time to a total reindexing? 💭

[sarayourfriend]

It might be possible, but upgrading between major versions doesn't allow you to do that, at least not 7 to 8. The data nodes use a separate block device, the SSD, that would be easy to image and restore from, but I don't know what benefit that gives us. We still need to test indexing against the new cluster anyway, so it's not like we could skip reindexing on staging and a data refresh.

[dhruvkb]

Looks good to me! A small nit but no blockers.