mirror of https://github.com/docker/docs.git
104 lines
4.0 KiB
Markdown
104 lines
4.0 KiB
Markdown
---
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description: How to run more than one process in a container
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keywords: docker, supervisor, process management
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redirect_from:
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- /engine/articles/using_supervisord/
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- /engine/admin/using_supervisord/
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title: Run multiple services in a container
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---
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A container's main running process is the `ENTRYPOINT` and/or `CMD` at the
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end of the `Dockerfile`. It is generally recommended that you separate areas of
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concern by using one service per container. That service may fork into multiple
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processes (for example, Apache web server starts multiple worker processes).
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It's ok to have multiple processes, but to get the most benefit out of Docker,
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avoid one container being responsible for multiple aspects of your overall
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application. You can connect multiple containers using user-defined networks and
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shared volumes.
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The container's main process is responsible for managing all processes that it
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starts. In some cases, the main process isn't well-designed, and doesn't handle
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"reaping" (stopping) child processes gracefully when the container exists. If
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your process falls into this category, you can use the `--init` option when you
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run the container. The `--init` flag inserts a tiny init-process into the
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container as the main process, and handles reaping of all processes when the
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container exits. Handling such processes this way is superior to using a
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full-fledged init process such as `sysvinit`, `upstart`, or `systemd` to handle
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process lifecycle within your container.
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If you need to run more than one service within a container, you can accomplish
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this in a few different ways.
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- Put all of your commands in a wrapper script, complete with testing and
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debugging information. Run the wrapper script as your `CMD`. This is a very
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naive example. First, the wrapper script:
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```bash
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#!/bin/bash
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# Start the first process
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./my_first_process -D
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status=$?
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if [ $status -ne 0 ]; then
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echo "Failed to start my_first_process: $status"
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exit $status
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fi
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# Start the second process
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./my_second_process -D
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status=$?
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if [ $status -ne 0 ]; then
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echo "Failed to start my_second_process: $status"
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exit $status
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fi
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# Naive check runs checks once a minute to see if either of the processes exited.
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# This illustrates part of the heavy lifting you need to do if you want to run
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# more than one service in a container. The container will exit with an error
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# if it detects that either of the processes has exited.
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# Otherwise it will loop forever, waking up every 60 seconds
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while /bin/true; do
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ps aux |grep my_first_process |grep -q -v grep
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PROCESS_1_STATUS=$?
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ps aux |grep my_second_process |grep -q -v grep
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PROCESS_2_STATUS=$?
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# If the greps above find anything, they will exit with 0 status
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# If they are not both 0, then something is wrong
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if [ $PROCESS_1_STATUS -ne 0 -o $PROCESS_2_STATUS -ne 0 ]; then
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echo "One of the processes has already exited."
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exit -1
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fi
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sleep 60
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done
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```
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Next, the Dockerfile:
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```conf
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FROM ubuntu:latest
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COPY my_first_process my_first_process
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COPY my_second_process my_second_process
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COPY my_wrapper_script.sh my_wrapper_script.sh
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CMD ./my_wrapper_script.sh
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```
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- Use a process manager like `supervisord`. This is a moderately heavy-weight
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approach that requires you to package `supervisord` and its configuration in
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your image (or base your image on one that includes `supervisord`), along with
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the different applications it will manage. Then you start `supervisord`, which
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manages your processes for you. Here is an example Dockerfile using this
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approach, that assumes the pre-written `supervisord.conf`, `my_first_process`,
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and `my_second_process` files all exist in the same directory as your
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Dockerfile.
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```conf
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FROM ubuntu:latest
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RUN apt-get update && apt-get install -y supervisor
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RUN mkdir -p /var/log/supervisor
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COPY supervisord.conf /etc/supervisor/conf.d/supervisord.conf
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COPY my_first_process my_first_process
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COPY my_second_process my_second_process
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CMD ["/usr/bin/supervisord"]
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```
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