HEALTHCHECK of a Docker container running Celery tasks?

The celery inspect ping command comes in handy, as it does a whole trip: it sends a “ping” task on the broker, workers respond and celery fetches the responses.

Assuming your app is named tasks.add, you may ping all your workers:

/app $ celery inspect ping -A tasks.add
-> celery@aa7c21dd0e96: OK
        pong
-> celery@57615db15d80: OK
        pong

With aa7c21dd0e96 being the Docker hostname, and thus available in $HOSTNAME.

To ping a single node, you would have to run:

celery inspect ping -A tasks.add -d celery@$HOSTNAME

Here, d stands for destination.

The line to add to your Dockerfile:

HEALTHCHECK CMD celery inspect ping -A tasks.add -d celery@$HOSTNAME

Sample outputs:

/app $ celery inspect ping -A tasks.add -d fake_node
Error: No nodes replied within time constraint.
/app $ echo $?
69

Unhealthy if the node does not exist or does not reply

/app $ celery inspect ping -A tasks.add -d celery@$HOSTNAME
-> celery@d39b3d31cc13: OK
        pong
/app $ echo $?
0

Healthy when the node replies pong.

/app $ celery inspect ping -d celery@$HOSTNAME
Traceback (most recent call last):
...
    raise socket.error(last_err)
OSError: [Errno 111] Connection refused
/app $ echo $?
1

Unhealthy when the broker is not available – I removed the app, so it tries to connect to a local AMPQ and fails
This might not suit your needs, the broker is unhealthy, not the worker.