Error-handling middleware for the docker-compose CLI. Greps through the stdout of a docker-compose command, finding the highest exit code produced by any services that exited prematurely. After docker-compose exits, prints the message associated with that highest code then exits with that code. Useful when you want to exit with an error code if …

docker-compose-shield.py

"""
Error-handling middleware for the docker-compose CLI. Greps through the stdout of a docker-compose command,
finding the highest exit code produced by any services that exited prematurely. After docker-compose
exits, prints the message associated with that highest code then exits with that code. Useful
when you want to exit with an error code if *any* of your containers fail, and not just if the one
specified by `--exit-code-from` fails.

Example usage:

```
docker-compose up --abort-on-container-exit | python3 <this-script>.py
```
"""
import re
import sys


def watch_then_exit_with_highest():
    highest_exit_code = 0
    exit_msg = "Shield detected no errors. Docker Compose completed successfully."
    for line in sys.stdin:
        # Matches "<docker-container-name> exited with code <code>"
        match = re.search(r"^\S+\sexited with code (\d+)$", line)
        if match:
            exit_code = int(match.group(1))
            if exit_code > highest_exit_code:
                highest_exit_code = exit_code
                exit_msg = line
        sys.stdout.write(line)
    return highest_exit_code, exit_msg.strip()


if __name__ == "__main__":
    code, msg = watch_then_exit_with_highest()
    if code > 0:
        print(
            f"Shield exiting with error code {code}, since this line was produced by docker compose:\n{msg}",
            file=sys.stderr
        )
    else:
        print(msg)
    sys.exit(code)