Framework for 0 downtime deploys

Confidential

Hello All

I wonder if I could garner some of the wealth of experience on this group:

Our current application deployments (every 3 weeks) require about 30min downtime. We are now tasked of making this 0 downtime.
From all the reading I have done, we have solutions for the infrastructure and code deploy, but with regards to the DB the main issue seems to be keeping the new deploy backwards compatible - functions/tables/fields - all of it.

That seems like quite a large management task and would require careful reviews of changes. Is there any type of framework that already manages this type of capability? Or are there aspects of PG that we should be using in this regard?

Thx

Z