Simplified Docker container hostname resolution

docker-hosts (yes, a terrible name) maintains a file in the format of /etc/hosts that contains IP addresses and hostnames of Docker containers. When the generated file is mounted at /etc/hosts within your Docker container it provides simple hostname resolution. This allows you to set up redis and web containers where the web container is able to connect to redis via its hostname. You can optionally provide a domain like dev.docker, so redis.dev.docker is a usable alias, as well.

This utility was inspired by Michael Crosby's skydock project. docker-hosts and skydock (paired with skydns) work in much the same way: the container lifecycle is monitored via the Docker daemon's events, and resolvable hostnames are made available to appropriately-configured containers. The end result is that you have a simple way of connecting containers together on the same Docker host, without having to resort to links or manual configuration. This does not provide a solution to container connectivity across Docker hosts. For that you should look at something like Jeff Lindsay's registrator.

building

This project uses gpm and gvp. Both must be available on your path.

make

-- or --

gvp init
source gvp in
gpm install
go build -v -o stage/docker-host ./...

running

Start the docker-host process and give it the path to a file that will be mounted as /etc/hosts in your containers:

docker-host /path/to/hosts

Optionally specify DOCKER_HOST environment variable.

Then start a container:

docker run -i -t -v /path/to/hosts:/etc/hosts:ro centos /bin/bash

Within the centos container, you'll see /etc/hosts has an entry for the container you just started, as well as any other containers already running. /etc/hosts will continue to reflect all of the containers currently running on this Docker host.

The only container that should have write access to the generated hosts file is the container running this application.

running in Docker

Create an empty file at /var/lib/docker/hosts, make it mode 0644 and owned by nobody:nobody.

docker run \
    -d \
    -v /var/run/docker.sock:/var/run/docker.sock \
    -v /var/lib/docker/hosts:/srv/hosts \
    blalor/docker-hosts --domain-name=dev.docker /srv/hosts