How to create a bidirectional link between containers?

Question

I have to link two containers so they can see each other. Of course the following...

docker run -i -t --name container1 --link container2:container2 ubuntu:t         


        

Answer 1

Here's how I've solved this for myself:

First, I go through all my containers (which need to know from each other) and create dnsmasq entries like so:

for f in container1 container2 container3; do
  IP=`docker inspect --format '{{ .NetworkSettings.IPAddress }}' $f 2>/dev/null`
  if [ -n "$IP" ]; then
    echo $f "$IP"
    echo "host-record=$f,$IP" > /etc/dnsmasq.d/0host_$f
  else
    rm -f /etc/dnsmasq.d/0host_$f
  fi
done

Then I start a dns container which has dnsmasq-base installed and starts the dnsmasq service:

docker run -d -P -h dns --name dns -v /etc/dnsmasq.d:/etc/dnsmasq.d:ro dns

then I get the IP address of this container:

DNS_IP=`docker inspect --format '{{ .NetworkSettings.IPAddress }}' dns`

And start the containers like so:

docker run -d -P -h container1 --name container1 --dns $DNS_IP container1
docker run -d -P -h container2 --name container2 --dns $DNS_IP container2
docker run -d -P -h container3 --name container3 --dns $DNS_IP container3

This is a simplified version of my setup but it shows the gist. I've also added a mechanism that forces dnsmasq to rescan when files in /etc/dnsmasq.d change via inotify-tools. That way all containers get the new ip address whenever one container is restarted.