task env: add NOMAD_UNIX_ADDR var

[gulducat]

I keep thinking of this, and finally I'm doin it. Allows for easier usage in task setup:

task "nomad-cli" {
  driver = "raw_exec"
  config { ... run `nomad` commands ... }
  identity {
    env = true
  }
  env {
    NOMAD_ADDR = "${NOMAD_UNIX_ADDR}"
    # instead of this, which requires you to know the right "unix://" prefix, and socket location
    NOMAD_ADDR = "unix://${NOMAD_SECRETS_DIR}/api.sock"
  }
}

I named it "_UNIX_ADDR" instead of "_ADDR_UNIX" because I figure there may be services out there called "UNIX" that would cause a name collision, but I'm open to other names.

E2E spot check on my linux laptop:

    --- PASS: TestTaskAPI/testTaskAPI_NomadCLI (1.12s)

[tgross]

"when using workload identity" doesn't quite feel like the right way to describe this. It's for use with workload identity. Maybe point out that it points to the Task API socket?

[tgross]

Aren't these usually of the form: unix://$PATH? ex. unix:///secrets/api.sock

[gulducat]

Right?? That's part of why this is all needed - the world is not consistent. With a caddy reverse proxy, for example, it's unix//path/to/sock 🤷

In our particular case, it can be either unix:{path} or unix://{path} (but not unix:/{path} nor unix/{path}).

Would you prefer unix://?

[tgross]

the world is not consistent

Yeah, there's no real standard here. The Go parser (which we're using in the api package) handles both https://go.dev/play/p/S2tCmK6la8H I think I'd prefer unix:// just because it matches the file:// URL scheme (from RFC1738 and friends). But that's a matter of taste.

[tgross]

Minor nit: this is a new feature, so it wouldn't get backported to 1.9.x/1.8.x