~/.dockerrc

We use Docker at work as part of our deployment strategy. Since we ship dockerized apps, Docker is part of our development environment. I develop in OS X, so I use Boot2Docker.

One of the original core contributors to Docker, @creack, was part of our team for a while. It was a great opportunity to get familiar with Docker as a technology. He helped me put together a ~/.dockerrc file that ensures my development environment is always ready to go. I source that ~/.dockerrc from my ~/.bashrc so that each new shell I open is wired up with docker.

Here’s the full ~/.dockerrc:

if [ ! `boot2docker status` = "running" ]; then
	boot2docker start > /dev/null
fi

if [ -z "$DOCKER_HOST" ]; then
	eval $(boot2docker shellinit 2>/dev/null)
	export DOCKER_IP=$(boot2docker ip 2> /dev/null)
fi

function rmi-docker() {
	docker images -q --filter 'dangling=true' | xargs docker rmi
}

function drop-containers() {
	docker ps -aq | xargs docker rm -fv
}

I’ll break down each section.

Auto-start

If boot2docker is not running for some reason, I want to start it.

if [ ! `boot2docker status` = "running" ]; then
	boot2docker start > /dev/null
fi

I’m not really interested in the output of boot2docker start, since this happens every time I open a new shell; so I pipe its STDOUT to /dev/null.

Environment Variables

The docker client relies on a few environment variables being set so that it knows where the docker daemon is running, and how to talk to it. At the moment, those variables are DOCKER_HOST, DOCKER_TLS_VERIFY, and DOCKER_CERT_PATH. boot2docker provides a handy shellinit command that spits out some contextual information on STDERR, and export commands for the environment variables it needs on STDOUT. Here’s what it looks like in my shell:

Writing /Users/tim/.boot2docker/certs/boot2docker-vm/ca.pem
Writing /Users/tim/.boot2docker/certs/boot2docker-vm/cert.pem
Writing /Users/tim/.boot2docker/certs/boot2docker-vm/key.pem
    export DOCKER_CERT_PATH=/Users/tim/.boot2docker/certs/boot2docker-vm
    export DOCKER_TLS_VERIFY=1
    export DOCKER_HOST=tcp://192.168.59.103:2376

If I were to just eval $(boot2docker shellinit), those first three lines would still show up in STDERR, so I silence those three lines with 2>/dev/null.

boot2docker also provides an ip command, which prints just the IP address from value it returns for DOCKER_HOST. It’s convenient to have it around, so I also assign it to DOCKER_IP.

This only needs to happen if DOCKER_HOST has not been set, so I put it in a conditional.

if [ -z "$DOCKER_HOST" ]; then
	eval $(boot2docker shellinit 2>/dev/null)
	export DOCKER_IP=$(boot2docker ip 2> /dev/null)
fi

Prune Dangling Images

After running docker build a number of times for the same project (making changes along the way), I tend to end up with a number of “dangling”—that is, untagged—Docker images. A majority of those images started FROM google/golang:1.4, and contain plenty of code vendored in Godeps… so they take up a lot of space. I wrote a function that just wraps a command to drop all of those dangling images.

function rmi-docker() {
	docker images -q --filter 'dangling=true' | xargs docker rmi
}

docker images lists all of the images on my machine, in a human-friendly table layout. The -q flag (for “quiet”) prints just the IDs of the images. --filter 'dangling=true' filters the list to show only the untagged images. I pipe that list to docker rmi, which deletes them.

Drop ALL THE CONTAINERS!

I’ve gotten better about cleaning up containers after they’ve stopped, but I still let a few fall through the cracks. I wrote a wrapper function that forcefully deletes all of the containers on my machine—even the running ones.

function drop-containers() {
	docker ps -aq | xargs docker rm -fv
}

docker ps will list the running containers on the machine in a table layout. The -a flag (for “all”) includes stopped containers, and the -q flag (for “quiet”) reduces the table layout to just a list of container IDs. I pipe that list to docker rm, which will delete stopped containers. I added the -f flag (for “force”) to delete the running containers as well, and I added the -v flag (for “verbose”) so that it lists the container IDs as it deletes them.