Yes, that's one of the major goals.
> We're using Postgres 9.4 on RDS right now, and there doesn't seem to be an upgrade path that doesn't involve some downtime.
Unfortunately on RDS your options are a bit more limited than on plain postgres. Otherwise you could use londiste, pglogical, .. to keep the time to switch over to something very small.
YMMV of course, better have your fingers crossed. If you don't trust it, do it the hard way: Switch to write-only mode (easiest: remove write rights for all DB users), notify your users, make a snapshot with pg_dump, restore to a fresh new DB copy and switch your services over. Worked for us, different story if you can't take any write downtime of course.
> A dump/restore using pg_dumpall, or use of pg_upgrade, is. > required for those wishing to migrate data from any previous > release.
This means no, I guess. This is what I don't get. How can anyone with a sizeable db in production do that?