I'm using docker 1.9.0 and I use docker network create to create 2 networks named 'net', 'net2', but when I started container, I tried to pass --net=net1 --net=net2 or --net=net1,net2 to join multi network before real process in container starts, I got failed.
I checked source code and I found allocateNetwork when allocate all networks in container.NetworkSettings.Networks, so it must be possible to do this, but how? It seems currently the API doesn't offer this feature.