« Running Docker on CentOS - External Network Access »

03 October 2014

This is just a short blip for people running Docker on CentOS who have encountered problems accessing containers from outside the localhost.

The long and short of it is this command:

$ sysctl net.ipv4.ip_forward=1

Why? Read this answer on StackExchange first. When Docker configures your iptables rules for network access, it likes to create a docker0 interface alongside any other network interfaces (like eth0) that CentOS creates by default.

Therefore, you must enable IP forwarding to allow those packets arriving on your externally-listening interface to be forwarded (or routed) to the docker interface that all of your containers are attached to.

Hopefully this helps somebody else out who may encounter similar problems.

ty@tjllgmail.net