Connecting to a remote dockerd on RancherOS on FreeNAS

2018-12-13

Last summer I migrated from an old QNAP NAS to FreeNAS. I also started using docker containers with RancherOS, via the FreeNAS-provided virtual machine image. I initially installed all my containers using the RancherOS cli (ssh into the machine), but now I am moving my container configurations out of the VM cli and versioning them so that I can at any point rebuild (or upgrade) the RancherOS disk image, and be able to reload all my containers. So I want to be able to run docker commands from my localhost cli, but have them be run on the RancherOS docker daemon.

Expose docker in RancherOS

To simplify life, copy your public ssh key to the RancherOS VM to enable passwordless login:

ssh-copy-id rancher@<rancheros-ip>

From MacOS with docker installed, run the following command to set up a docker connection from localhost to RancherOS, as well as magically open dockerd for TCP connections on port 2376 on the RancherOS VM:

docker-machine create \
  --driver generic \
  --generic-ip-address=<rancheros-ip> \
  --generic-ssh-key ~/.ssh/id_rsa \
  --generic-ssh-user=rancher \
  rancheros-docker

To verify the new machine configuration was created run the following:

$ docker-machine ls
NAME               ACTIVE   DRIVER    STATE     URL                         SWARM   DOCKER        ERRORS
rancheros-docker   *        generic   Running   tcp://<rancheros-ip>:2376           v17.09.1-ce

Use docker from RancherOS on localhost

Switch the docker context to the newly created docker machine configuration:

eval "$(docker-machine env rancheros-docker)"

Now, any docker commands will be executed on the RancherOS docker, not localhost.

Reset docker on localhost back to defaults

To reset localhost back to normal (use the locally installed docker):

eval "$(docker-machine env -u)"

Upcoming changes

Starting with Docker 18.09, connecting to a remote docker can be done much more easily as ssh connections are supported in the DOCKER_HOST variable! So that means all of the above can be replaced by just a simple export:

export DOCKER_HOST=ssh://rancher@<rancheros-ip>

This will require Docker 18.09 both locally and on the RancherOS VM, but it looks it will be a while before both RancherOS and FreeNAS have 18.09 available. The latest stable FreeNAS 11.2 has RancherOS 1.4.2, which has Docker 18.06, perhaps FreeNAS 11.3?