Run Rails migrations as Kubernetes jobs

[willtcarey]

Reading through this article https://www.honeybadger.io/blog/rails-on-kubernetes/.

They do a really nice thing of running the Rails migrations as a Kubernetes job. That just....makes sense.

Cons of our current setup is

• Application is prevented from starting up while migrations are running
• ^Because of the above long running migrations are pretty dangerous. Those translate to application downtime.
• Extra code has to be added to every application.rb

Pros of running it as a job

• We can run the migrations before we even tear down old instances of the application meaning no downtime.

Cons of running it as a job

• All migrations must be backwards compatible.
• You can't remove a column that the application still depends on in a migration because that old instance of the application will still be running. You have to make a migration that adds a new column and changes the code to rely on that new column, then make a new deployment which cleans up the old database column. This is a pretty common paradigm in large scale applications.