4.2. Run a Docker Container#

In the 4.1. Docker Quick Start lab you created and destroyed a container for Dokuwiki. In this lab we will change the docker run command so that we can:

  1. Configure environment variables in DokuWiki

  2. Store DokuWiki data permanently on the filesystem

  3. Open network ports to the container

Store Data#

The most common way to store data in Docker is to create a volume mount that shares a directory in the container with a directory on the host. You can have as many shared directories as you like using the -v option:

docker run -v /path/on/host:/path/in/container

The /path/on/host MUST be an absolute path. So it’s common to see this shell trick:

docker run -v $(pwd)/host-path:/app/container-path

Set Environment Variables#

Containers are configured with the environment. Setting variables is simple:

docker run -e ENV_VAR="value"

Network Ports#

In the quickstart we created a container that had exposed ports. The format of the -p option is:

-p host-port:container-port

So this example connect’s the host’s port 8080 to the container port 80:

-p 8080:80

There can be multiple ports.

User and Group#

Docker container run as root. It might seem counterintuitive that a container have high privileges, but it’s important to remember that a container is not a security boundary, it’s for convenience. It’s best to reduce the privileges of a container with the -u or --user argument. It specifies the user and group ID of the container. For example:

# Run as user 1000 and group 1000
$ docker run -u 1000:1000 ...

There’s a nice shell trick to make the container run as you:

$ docker run -u $(id -u):$(id -g) ...

Run Configuration for Dokuwiki#

Containers are expendable. When run with the --rm option, the container will be automatically deleted when it stops. That’s a nice way to not have to clean up. To run Dokuwiki with durable storage, a pre-set password and an exposed port run:

$ mkdir ~/dokuwiki
$ docker run -it --rm \
    -u $(id -u):$(id -g) \
    -p 8080:8080 \
    -e DOKUWIKI_PASSWORD=student \
    -e DOKUWIKI_USERNAME=student \
    -v $HOME/dokuwiki:/storage \
    dokuwiki/dokuwiki:stable

Cleanup#

You can delete the container image, but keep the data with docker rm. It’s not necessary but you you want to get rid of Dokuwiki’s data:

$ sudo rm -rf ~/dokuwiki/