Use a specific outbound IP with Docker

I have 3 network interfaces: docker0, eth0 and eth0:0 (alias).

    auto eth0
      iface eth0 inet static
      address 1.2.3.4
      netmask 255.255.255.0
      network 1.2.3.0
      broadcast 1.2.3.255
      gateway 1.2.3.254

    auto eth0:0
      iface eth0:0 inet static
      address 5.6.7.8
      netmask 255.255.255.255
      broadcast 5.6.7.8

docker0 is the bridge auto created by docker.

What's the easiest way to make Docker and all its containers use the outbound IP 5.6.7.8 instead of 1.2.3.4?

Solution 1:

It appears there is no easy way to do it with docker - at the moment at least.

What I ended up doing is simply using SNAT:

 iptables -t nat -I POSTROUTING -p all -s 172.17.0.0/16 -j SNAT --to-source 5.6.7.8

172.17.0.0/16 is the subnet used by docker0.

Solution 2:

Use the --ip command line parameter.

# echo 'DOCKER_OPTS="$DOCKER_OPTS --ip=5.6.7.8"' >> /etc/default/docker
# docker help
...
  --ip=0.0.0.0     Default IP address to use when binding container ports