Container continues to run silently when cos-alerter fails

[IbraAoad]

Issue

Fixes #38

Solution

If no configuration file is passed, the code now catches a FileNotFoundError and exits with a non-zero exit status.

Testing Instructions

1. Run the following command:
   docker run -p 8080:8080 ghcr.io/canonical/cos-alerter:latest
2. Verify that cos-alerter fails to start and observe the following output:

2024-03-07T17:09:29.587Z [pebble] Started daemon.
2024-03-07T17:09:29.601Z [pebble] POST /v1/services 7.02659ms 202
2024-03-07T17:09:29.602Z [pebble] Started default services with change 1.
2024-03-07T17:09:29.611Z [pebble] Service "cos-alerter" starting: /usr/bin/cos-alerter
2024-03-07T17:09:29.915Z [cos-alerter] Config file not found. Exiting...
2024-03-07T17:09:29.960Z [pebble] [change 1 "Start service \"cos-alerter\"" task] failed: cannot start service: exited quickly with code 1

[lucabello]

CI's failing because it's checking for the line you removed in rockcraft.yaml.
Before merging, can you first fix it (pull-request.yaml) by replacing the line:

rock_pkg_version=$(grep -P -o 'cos-alerter==\d+\.\d+\.\d+' rockcraft.yaml | grep -P -o '\d+\.\d+\.\d+')

with

rock_pkg_version=$(grep -P -o -m 1 'version: "\d+\.\d+\.\d+"' rockcraft.yaml | grep -P -o '\d+\.\d+\.\d+')

(note: it's likely gonna fail on this PR again, but at least the next ones will be okay)

[IbraAoad]

CI's failing because it's checking for the line you removed in rockcraft.yaml. Before merging, can you first fix it (pull-request.yaml) by replacing the line:

rock_pkg_version=$(grep -P -o 'cos-alerter==\d+\.\d+\.\d+' rockcraft.yaml | grep -P -o '\d+\.\d+\.\d+')

with

rock_pkg_version=$(grep -P -o -m 1 'version: "\d+\.\d+\.\d+"' rockcraft.yaml | grep -P -o '\d+\.\d+\.\d+')

(note: it's likely gonna fail on this PR again, but at least the next ones will be okay)

I think it's safe to remove the line entirely since this check is already implemented in rock_version?

[lucabello]

True! Approving :)