Registrator

Service Registrator for Docker with DNS interface.

Registrator automatically registers and deregisters services for any Docker container by inspecting containers as they come online. Registrator provides a DNS interface for external systems to query for the IP address and exposed port of a registered service.

Running Registrator

The quickest way to see Registrator in action is running locally with docker-machine. Typically, running Registrator looks like this:

$ docker run -d \
  	     --name=registrator \
     --volume=/var/run/docker.sock:/tmp/docker.sock \
     -p 5555:5555/udp \
     barbct5/registrator:latest

First we run the container detached and name it registrator. We also mount the Docker socket inside in the container so the Registrator service can listen for Docker lifecycle events. You should be able see the logs for Registrator

$ docker logs registrator

Running Redis

As you start containers, if they provide a service, they will be added to the service registry. Let's try running redis in a container:

$ docker -d --name=redis -P redis

We run the redis container detached and expose all defined ports in the Dockefile and let Docker assign a random port on the host. Since Registrator provides service discovery for external systems, the host port doesn't matter. You can find the newly started redis service:

   $ dig @$(docker-machine ip dev) -p 5555 ANY _redis._tcp.example.com

   ;; Warning: query response not set

   ; <<>> DiG 9.8.3-P1 <<>> @127.0.0.1 -p 5555 ANY _redis._tcp.example.com
   ; (1 server found)
   ;; global options: +cmd
   ;; Got answer:
   ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 6333
   ;; flags: rd; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 0
   ;; WARNING: recursion requested but not available

   ;; QUESTION SECTION:
   ;_redis._tcp.example.com.	IN	ANY

   ;; ANSWER SECTION:
   _redis._tcp.example.com. 0	IN	A	192.168.99.100
   _redis._tcp.example.com. 0	IN	SRV	10 10 32770 192.168.99.100.

   ;; Query time: 0 msec
   ;; SERVER: 127.0.0.1#5555(127.0.0.1)
   ;; WHEN: Mon Dec 21 12:29:53 2015
   ;; MSG SIZE  rcvd: 91

With the IP address and port for the redis service running the container we can connect via the cli:

$ redis-cli -h 192.168.99.100 -p 32770

Building

We use rebar3 as the standard build tool for Registrator. To compile and build a release:

$ ./rebar3 release

We can build a Docker image:

$ docker build --tag registrator:latest .