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bring swiftrepl back to life
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While the decision seemingly wasn't documented anywhere when it was made, it seems swiftrepl was turned off as part of T204245: Run MediaWiki media originals active/active.

We should bring it back to life, adding some logging on the case where a file wasn't already replicated (as unlike in its previous life, that's now unexpected).

This task does not have fixing T162123: Running swiftrepl is not puppetized in its immediate scope.

Event Timeline

Change 531964 had a related patch set uploaded (by CDanis; owner: CDanis):
[operations/software@master] Re-enable logging of files needing to be synced, since this is now unexpected in a post-active/active world.

Fano removed a subscriber: Fano.Sat, Aug 24, 3:15 AM

Change 532793 had a related patch set uploaded (by CDanis; owner: CDanis):
[operations/software@master] swiftrepl: bring close to as-is in production

aaron added a comment.Wed, Aug 28, 8:02 AM

I do worry about the risk of data loss if swiftrepl is also deleting files based on container list differences.

Between some FileBackendMultiWrite cleanup, LocalFileBatch* refactoring, and possibly making ?action=purge trigger FileBackendMultiWrite (no patch for that last one yet), maybe that would enough.

Change 532793 merged by jenkins-bot:
[operations/software@master] swiftrepl: bring close to as-is in production

Change 531964 merged by jenkins-bot:
[operations/software@master] swiftrepl: log on replications

Mentioned in SAL (#wikimedia-operations) [2019-09-05T14:11:02Z] <cdanis> restarted swiftrepl on ms-fe1005 T231110

Leaving some notes here before I'm gone for two weeks.

  • The script as it exists on ms-fe1005:/srv/swiftrepl matches git master, and works. Kinda.
  • I modified (which is not in git) to have a slightly different naming format for its log files.
  • I modified (ditto) to not run cross-cluster deletes, out of paranoia.
  • There's a logic error in handling some of the containers: P9064 I did not have time to get to the bottom of this. Instead I just quit that swiftrepl instance when it reached that state, and the wrapper script continued on to other containers.
  • There were a _lot_ of Etag mismatches for the thumbnail containers. In those cases I also quit the script and moved on. I'm assuming the cause is simply that thumbor isn't 100% deterministic, and that no harm is actually being done by replicating the other versions, but I do not actually know either of those things for sure. (Also: maybe, in the grand scheme of things, replicating thumbnails is just unnecessary?)

I think next steps are to debug/bandaid the issue where gets stuck, and do some Puppetization to do a git clone, and also to create a systemd service+timer, running in both eqiad and codfw.

Change 536586 had a related patch set uploaded (by Filippo Giunchedi; owner: Filippo Giunchedi):
[operations/puppet@production] WIP swift: add swiftrepl