Write a healthcheck to a contract

Situation

The deploy does not send traffic to a new app version right away: first it asks the ~/bash-lab/healthcheck.sh script whether the address is ready. The deploy looks at the exit status, the on-call engineer reads the output line. The script does not exist yet — there is a stub with a shebang line.

A test app runs on the machine for your experiments, http://127.0.0.1:8181:

Nothing listens on port 8182.

Task

Finish ~/bash-lab/healthcheck.sh to the contract with the deploy:

1. The deploy runs the script by its path: ~/bash-lab/healthcheck.sh URL.
2. The server answered 200 — the script prints the line OK to stdout and exits with 0.
3. The server answered anything else (503, 204, 302, 404) — FAIL and exit status 1. The script does not follow a redirect.
4. The server refuses the connection — FAIL and exit status 1.
5. No response for 2 seconds — FAIL and exit status 1; the script ends by itself within 3 seconds.
6. No address or two arguments — empty stdout, the line Usage: healthcheck.sh URL on stderr, exit status 2.

When the server answered — with any code — stderr stays empty: the deploy treats a line there as a failure of the check itself.

The check runs your script as student on these addresses and on its own — with other paths and responses.

The machine has no Internet; everything you need is already installed.