Liveness and health probes

[pdelaby]

As we use imgpush with Docker, it could be interesting to add liveness and readiness endpoints (for Docker Healthcheck and/or Kubernetes probes.

Liveness

Usually a simple GET request on a specific endpoint does the trick. I would suggest creating a /liveness endpoint that just returns 200 OK.

Something like

@app.route("/liveness", methods=["GET"])
def liveness():
    return Response(status=200)

For the container to be able to query it, the image woud need to install curl in order to perform the check :

• either directly in the Dockerfile : (not yet supported by Kubernetes I think)

HEALTHCHECK CMD curl http://localhost:5000/liveness -s -f -o /dev/null || exit 1

• or in the docker-compose

    healthcheck:
      start_period: 0s
      test: ['CMD-SHELL', 'curl localhost:5000/liveness -s -f -o /dev/null || exit 1']
      interval: 30s

Readiness

For this one, I'm more mitigated. I really like the Spring Health Actuator ( see example here ) that check evyrthing the app depends on. In this case, maybe the disk space ?

The /health endpoint coud return something like

{ 
   "status":"UP",
   "diskspace":{ 
      "status":"UP",
      "free":912412675,
      "treshold":10485260,
      "total":5512411672
   }
}

And diskspace woud be DOWN when the free space is below the diskspace_threshold setting.

However, this is not a free operation (that's why I suggest to use /liveness for Docker health), and probably needs to be cached and/or secured. The lib py-healthcheck does the caching job pretty well, and the endpoint coud be hidden from public access, but it's a more sensitive issue than the readiness endpoint.

What do you think ?

[hauxir]

Sounds useful. I'm not too familiar with kubernetes probes but if you are and you need this feature, feel free to open up a PR and i'll have a look :)