Look in more directories for upgrade binaries

[cbandy]

Checklist:

• Have you added an explanation of what your changes do and why you'd like them to be included?
• Have you updated or added documentation for the change, as applicable?
• Have you tested your changes on all related environments with successful results, as applicable?
  • Have you added automated tests?

Type of Changes:

• New feature

What is the current behavior (link to any open issues here)?

Images for major upgrades must have binaries at Red Hat paths.

What is the new behavior (if this is a feature change)?

Major upgrades look for binaries in typical paths for multiple distro flavors: Alpine, Debian, Red Hat.

Other Information:

Issue: PGO-864

[sfc-gh-jmckulka]

Maybe describe what is going on here a little more.

My understanding is that the postgres.ShellPath stuff sets the path variable and the command -v postgres/initdb returns the full path to the binary

[cbandy]

👍🏻 I've added some description.

That made me realize the PATH built into the image is also searched, so any ol' postgres might be found. I added an assertion* on the --version returned by something in old_bin and new_bin, and learned and doc'd that pg_upgrade does a similar check only recently-ish.

* same check as the postgres init container:

postgres-operator/internal/postgres/config.go

Lines 489 to 491 in e395e2a

	`results 'postgres version' "${postgres_version:=$(postgres --version ||:)}"`,
	`[[ "${postgres_version}" =~ ") ${expected_major_version}"($|[^0-9]) ]] ||`,
	`halt Expected PostgreSQL version "${expected_major_version}"`,

[sfc-gh-jmckulka]

With this change do we need the postgres bins on the PATH in the image level 🤔

[cbandy]

With this change do we need the postgres bins on the PATH in the image level 🤔

PGUpgrade (upgrade image) should work without it after this, but PostgresCluster (postgres image) still relies on the image PATH.