While working on a project with EdgeDB1 and FastAPI2, I wanted to perform health checks against the FastAPI server in the GitHub CI. This would notify me about the working state of the application. The idea is to:

  • Run the server in the background.
  • Run the commands against the server that’ll denote that the app is in a working state.
  • Perform cleanup.
  • Exit with code 0 if the check is successful, else exit with code 1.

The following shell script demonstrates a similar workflow with a Python HTTP server. This script:

  • Runs a Python web server in the background.
  • Makes an HTTP request against the server and checks if it returns HTTP 200 (OK). If the request fails or the server isn’t ready then waits for a second and makes the request again, and keeps retrying for the next 20 times before giving up.
  • Performs cleanups and kills the Python processes.
  • Exit with code 0 if the request is successful, else exit with code 1.
#!/bin/bash

set -euo pipefail

# Run the Python server in the background.
nohup python3 -m http.server 5000 >> /dev/null &

# Give the server enough time to be ready before accepting requests.
c=20
while [[ $c != 0 ]]
do
    # Run the healthcheck.
    if [[ $(curl -I http://localhost:5000/ 2>&1) =~ "200 OK" ]]; then
        echo "Health check passed!"

        # ...do additional cleanups if required.
        pkill -9 -i python
        exit 0
    fi
    ((c--))
    echo "Server isn't ready. Retrying..." $c
    sleep 1
done

echo "Health check failed!"
# ...do additional cleanups if required.
pkill -9 -i python
exit 1

The nohup before the python3 -m http.server 5000 makes sure that the SIGHUP signal can’t reach the server and shut down the process. The ampersand & after the command runs the process in the background. Afterward, the script starts making requests to the http://localhost:5000/ URL in a loop. If the server returns HTTP 200, the health check is considered successful. This will break the loop and the script will be terminated with exit 0 status. If the server doesn’t return HTTP 200 or isn’t ready yet, the script will keep retrying 20 times with a 1 second interval between each subsequent request before giving up. A failed health check will cause the script to terminate with exit 1 status.

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