Health Check command for docker(1.12) container (Not in Dockerfile!)

Question

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

Answer 1

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.

Answer 2

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!

Answer 3

The Docker inspect command lets you view the output of commands that succeed or fail

docker inspect --format='{{json .State.Health}}' your-container-name