I'm guessing =~ is a RegExp match and ! at the front negates it... but what does -? mean here?

Seems like copy-pasted code from somewhere that was supposed to handle negative numbers, but in our case version numbers are positive only

Capitalize Docker

Why is there a space after index?

Same question about -?

Weird indentation here again

Indentation issues here

Nit – I find it helpful to use some kind of "more important" style for these header comments. One example in our codebase is the keyserver's Dockerfile (link), but we don't really have a standard / consistent style for it

If I recall correctly, some of the migration logic was handled "inside" Terraform. I vaguely recall that the terraform apply would internally make sure to bring up the secondary services only after the primary completed the migration.

Two things here:

1. It would be helpful to the reader of this script to have some explanation of that, and a pointer to where the code for it is
2. How does the "internal" logic inside Terraform differentiate between the terraform apply here, versus the one on line 197? In the former case, we want to wait on the primary before bringing the secondary online; in contrast, in the latter case we want to immediately update all tasks