What tools and processes do you use for this? Are there any established best practices?
For more context, I'm using a managed SQL database and the application runs on Kubernetes.
Make alter table statements, depending on the engine some can be non-locking/blocking.
Deploy code.
Enjoy.
First add the additions to the db, then the new version of the software can work with the db.
Then once all software is updated, remove the old fields.