How to keep Docker container running after startin

Question

I've seen a bunch of tutorials that seem do the same thing I'm trying to do, but for some reason my Docker containers exit. Basically, I'm setting up a web-server and a few daemons inside a Docker container. I do the final parts of this through a bash script called run-all.sh that I run through CMD in my Dockerfile. run-all.sh looks like this:

service supervisor start
service nginx start

And I start it inside of my Dockerfile as follows:

CMD ["sh", "/root/credentialize_and_run.sh"]

I can see that the services all start up correctly when I run things manually (i.e. getting on to the image with -i -t /bin/bash), and everything looks like it runs correctly when I run the image, but it exits once it finishes starting up my processes. I'd like the processes to run indefinitely, and as far as I understand, the container has to keep running for this to happen. Nevertheless, when I run docker ps -a, I see:

➜  docker_test  docker ps -a
CONTAINER ID        IMAGE                            COMMAND                CREATED             STATUS                      PORTS               NAMES
c7706edc4189        some_name/some_repo:blah   "sh /root/run-all.sh   8 minutes ago       Exited (0) 8 minutes ago                        grave_jones

What gives? Why is it exiting? I know I could just put a while loop at the end of my bash script to keep it up, but what's the right way to keep it from exiting?

Answer 1

Capture the PID of the ngnix process in a variable (for example $NGNIX_PID) and at the end of the entrypoint file do

wait $NGNIX_PID 

In that way, your container should run until ngnix is alive, when ngnix stops, the container stops as well

Answer 2

The reason it exits is because the shell script is run first as PID 1 and when that's complete, PID 1 is gone, and docker only runs while PID 1 is.

You can use supervisor to do everything, if run with the "-n" flag it's told not to daemonize, so it will stay as the first process:

CMD ["/usr/bin/supervisord", "-n"]

And your supervisord.conf:

[supervisord]
nodaemon=true

[program:startup]
priority=1
command=/root/credentialize_and_run.sh
stdout_logfile=/var/log/supervisor/%(program_name)s.log
stderr_logfile=/var/log/supervisor/%(program_name)s.log
autorestart=false
startsecs=0

[program:nginx]
priority=10
command=nginx -g "daemon off;"
stdout_logfile=/var/log/supervisor/nginx.log
stderr_logfile=/var/log/supervisor/nginx.log
autorestart=true

Then you can have as many other processes as you want and supervisor will handle the restarting of them if needed.

That way you could use supervisord in cases where you might need nginx and php5-fpm and it doesn't make much sense to have them apart.

Answer 3

This is not really how you should design your Docker containers.

When designing a Docker container, you're supposed to build it such that there is only one process running (i.e. you should have one container for Nginx, and one for supervisord or the app it's running); additionally, that process should run in the foreground.

The container will "exit" when the process itself exits (in your case, that process is your bash script).

---

However, if you really need (or want) to run multiple service in your Docker container, consider starting from "Docker Base Image", which uses runit as a pseudo-init process (runit will stay online while Nginx and Supervisor run), which will stay in the foreground while your other processes do their thing.

They have substantial docs, so you should be able to achieve what you're trying to do reasonably easily.

Answer 4

Make sure that you add daemon off; to you nginx.conf or run it with CMD ["nginx", "-g", "daemon off;"] as per the official nginx image

Then use the following to run both supervisor as service and nginx as foreground process that will prevent the container from exiting

service supervisor start && nginx

In some cases you will need to have more than one process in your container, so forcing the container to have exactly one process won't work and can create more problems in deployment.

So you need to understand the trade-offs and make your decision accordingly.

Answer 5

I just had the same problem and I found out that if you are running your container with the -t and -d flag, it keeps running.

docker run -td <image>

Here is what the flags do (according to docker run --help):

-d, --detach=false         Run container in background and print container ID
-t, --tty=false            Allocate a pseudo-TTY

The most important one is the -t flag. -d just lets you run the container in the background.

Answer 6

If you are using a Dockerfile, try:

ENTRYPOINT ["tail", "-f", "/dev/null"]

(Obviously this is for dev purposes only, you shouldn't need to keep a container alive unless it's running a process eg. nginx...)