Port forwarding in docker-machine?

Since boot2docker is deprecated I've switched to docker-machine but I don't know how to open a port from docker-machine. In boot2docker I could do like this:

boot2docker ssh -L 27017:localhost:27017

This would forward port 27017 from VirtualBox to localhost 27017 as long as the SSH connection is open. Note that I'm not looking for a way to open the port permanently in VirtualBox. How can I achieve this with docker-machine?

You can still access the VBoxmanage.exe command from the VirtualBox used by docker machine:

VBoxManage controlvm "boot2docker-vm" natpf1 "tcp-port27017,tcp,,27017,,27017";

• Use docker-machine info to get the name of your vm.
• use modifyvm if the vm isn't started yet.

See a practical example in this answer.

That is the current workaround, pending the possibility to pass argument to docker-machine ssh: see issue 691.

The other workaround is to not forward port, and use directly the IP of the VM:

 $(docker-machine ip default)

As commented by sdc:

You can confirm that port forwarding is set up correctly with

 VBoxManage showvminfo boot2docker-vm | grep "NIC.* Rule" 

With recent versions of machine, you can simply do (where default is the name of the machine):

docker-machine ssh default -L 27017:localhost:27017

This is a more temporary solution than the VM configuration change.

Use the following variation to only forward ports in a background process:

docker-machine ssh default -f -N -L 27017:localhost:27017

• -f Requests ssh to go to background just before command execution.
• -N Allow empty command (useful here to forward ports only)

You can ssh into the machine and pass on the regular port forwarding arguments:

ssh docker@$(docker-machine ip default) -L 27017:localhost:27017

The password of the docker user is tcuser. (see https://github.com/boot2docker/boot2docker)