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Docker Version 1.12, I got a Dockerfile from Here

FROM nginx:latest

RUN touch /marker

ADD ./check_running.sh /check_running.sh
RUN chmod +x /check_running.sh

HEALTHCHECK --interval=5s --timeout=3s CMD ./check_running.sh

I'm able to roll the updates and health checks with check_running.sh shell script. Here, the check_running.sh script is copied to image, so the launched container has it.

Now, my question is there any way to Health Check from out side of the container and script also located outside.

I'm excepting a health check command to get the container performance(Depends on what we wrote in script), IF the container is not performing good it should roll-back to previous version ( Kind of a process that monitors the containers, if it is not good, it should roll-back to previous)

Thanks

Veerendra K
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5 Answers5

5

is there any way to Health Check from out side of the container and script also located outside.

Kind of a process that monitors the containers, if it is not good, it should roll-back to previous

You have several options:

  1. From outside, you run a process inside the container to check its health with docker exec. This could be any sequence of shell commands. If you want to keep your scripts outside of the container, you might use something like cat script.sh | docker exec -it container sh -s.
  2. You check the container health from outside the container, e.g. by looking for a process that should be running inside the container (try to set a security profile and use ps -Zax or try looking for children of the daemon), or you can give each container a specific user ID with --user 12345 and then look for that or e.g. connecting to its services. You'd have to make sure it's running inside the right container. You can access the containers' filesystem below /var/lib/docker/devicemapper/mnt/<hash>/rootfs.
  3. You run a HEALTHCHECK inside the container and check its health with docker inspect --format='{{json .State.Health.Status}}' <containername> combined with e.g. a line in the Dockerfile: HEALTHCHECK CMD wget -q -s http://some.host to check the container has internet access.

I'd recommend option 3, because it's likely to be more compatible with other tools in the future.

Dej
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    Regarding option 3: Do not execute this every 5 seconds. It would be crazy if 1 million users of your container, connect every 5 seconds to a website ;) – mgutt Oct 09 '20 at 12:11
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Just got comment from a blog!. He refered Docker documentation HealthCheck section. There is a health check "option" for docker command to "override" the dockerfile defaults. I have not checked yet!. But it seems good for me to get what I want. Will check and update the answer!

Veerendra K
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    The `docker run --health-cmd ...` is just overriding the value of the Dockerfile's `HEALTHCHECK`. It doesn't change where the scripts runs, mainly, inside the container. – BMitch Aug 16 '16 at 18:07
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The Docker inspect command lets you view the output of commands that succeed or fail

docker inspect --format='{{json .State.Health}}' your-container-name
f-society
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That's not available with the Dockerfile HEALTHCHECK option, all checks run inside the container. To me, this is a good thing since it avoids potentially untrusted code running directly on the host, and it allows you to include the dependencies for the health check inside your container.

If you need to monitor your container from outside, you'll need to use another tool or monitoring application, there are quite a few of them out there.

BMitch
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You can view the results of the health check by running docker inspect on a container.

Another approach depending on your application would be to expose a /healthz endpoint that the healthcheck also probes, this way it can be queried externally or internally as needed.

StephenKing
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Ahmed Elsabbahy
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