Love is a highway, maybe docker should be as well?

This is an unstructered attempt at getting some ease of use into docker service discovery of both local (dev) and clustered (production) containers.

Well, it's not certain that you do. This switches the usual linking between docker containers for an off-brand etcd backed solutions.

This allows you to not worry about linking between containers, but instead of $linkname_PORT_xyz_TCP_ADDR:$linkname_PORT_xyz_TCP_PORT can say container_name.local. It also enables you to continue this practice for containers running on non-local machines.

It consists of several components:

• etcd
• Haproxy + confd
• dnsmasq

Combined, this allows us to store docker containers' ip+port address in etcd, saved under the name of the container we can use haproxy to match host headers and resolve the containers based on URLs. Cherry on top is dnsmasq, which enables us to do all of this on the docker daemon address (default 172.17.42.1).

Running this is the easy bit:

make

This will boot 4 containers, assuming that ports 80 and 53 are available on your system.

Next comes the DNS resolving. To enable intra-container communication with this scheme you must use the --dns flag either on all containers you start or on your docker daemon. The value of this should be the ip of your docker network. This can be specified on your daemon, default is 172.17.42.1, so:

--dns 172.17.42.1

Now, in order for containers to be resolvable bind the service you want to advertise to the docker network ip. For instance for port 9090:

-p 172.17.42.1::9090

To be able to use the same address to reach machines from your own machine you have to have 127.0.0.1 in your list of dns nameservers. Objective is to have this in /etc/resolv.conf, the road to achieve this varies greatly between setups. Please consult your manual

Only supports http services, because of the header based approach. This can be extrapolated to known ports for tcp, but it would require us to run everything with --net=host, which brings a series of side effects.