Import fails when using S3 for Merge Request Diffs
When using Object Storage for Merge Request Diffs, the Sidekiq nodes get confused and fail.
Steps to reproduce
From a large prospect:
We have multiple servers behind a load balancer. And we're using
gitlab_rails['external_diffs_enabled'with S3 storage. Some of the import sidekiq jobs are failing attempting to find a merge request diff in
/var/opt/gitlab/gitlab-rails/shared/external-diffs/. Sure enough, there are some files in this directory on our multiple machines. It kinda looks like one job creates a local file then another job runs to try to upload it to S3. But the job runs on a separate machine and can't find the local file! We can work around by stopping the sidekiq jobs on all but 1 machine so local files are only written to one server. I suppose we could also use an NFS mount for
A related issue is that all of the files are going into a single directory. We have >250,000 files in a directory. Most filesystems have scaling issues with that many files in a directory. It would be a good idea to shard the files across hundreds of directories so there is an upper bound on number of files in a directory.