Investigate using pg_logical for upgrading PostgreSQL without downtime
Starting with PostgreSQL 9.4 one can use pg_logical for logical replication between different PostgreSQL versions. Per PostgreSQL 10.0 this extension is included by default if I'm not mistaken.
We should investigate how we'd go about upgrading PostgreSQL using this extension, what the drawbacks are, how we can automate it, etc. Once we know more we can determine how to include this into Omnibus (if at all).