Also would like to know this. This post is a bit light on content. It sounds like they just moved to K8s from RDS. In my experience, Postgres works decently but there are sharp edges running it containerized (OOMS in subprocesses might not be caught by the container runtime, shared memory is pitifully low in docker at 64 MB by default)

From other comments, it looks like they rolled their own solution. Perhaps they had unique requirements, but it seems short-sighted to forego the automation an operator brings.