At Teem, we aim for zero down-time deploys; so, one of the most important things we must validate is that things will not break mid-deploy!
The most sensitive step of the deploy process is the changes to our database. Prior to the automation I am about to describe, validation of the database migrations required specialized knowledge about Postgres, the changes to the application model, load on the database for that model, and a bit of general experience. This obviously slows down reviews and subsequently deploys. Worse, it was simply too easy to miss problem migrations when depending on only peer reviews. To make our lives easier we created a series of validation checks to ensure that each database migration will be backwards compatible.