Commit e18b4948 authored by Mike Jang's avatar Mike Jang

Merge branch 'es-migration-docs-multi-version' into 'master'

Add some Elasticsearch migration docs about version compatibility

See merge request gitlab-org/gitlab!54284
parents 13669664 99151296
......@@ -242,6 +242,27 @@ class BatchedMigrationName < Elastic::Migration
end
```
### Multi-version compatibility
These Elasticsearch migrations, like any other GitLab changes, need to support the case where
[multiple versions of the application are running at the same time](multi_version_compatibility.md).
Depending on the order of deployment, it's possible that the migration
has started or finished and there's still a server running the application code from before the
migration. We need to take this into consideration until we can [ensure all Elasticsearch migrations
start after the deployment has finished](https://gitlab.com/gitlab-org/gitlab/-/issues/321619).
### Reverting a migration
Because Elasticsearch does not support transactions, we always need to design our
migrations to accommodate a situation where the application
code is reverted after the migration has started or after it is finished.
For this reason we generally defer destructive actions (for example, deletions after
some data is moved) to a later merge request after the migrations have
completed successfully. To be safe, for self-managed customers we should also
defer it to another release if there is risk of important data loss.
## Performance Monitoring
### Prometheus
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