How is a Docker Machine marked as active?

Question

I am working through the Docker Machine User Guide over at https://docs.docker.com/v1.5/machine/.

It says:

You can see the machine you have created by r         


        

Answer 1

Its' pretty simple and the answer lies in the statement "a machine is considered active if the DOCKER_HOST environment variable points to it" from docker website: https://docs.docker.com/machine/reference/active/

So, let's say initially:

$ docker-machine ls

NAME      ACTIVE   DRIVER         STATE     URL
dev       -        virtualbox     Running   tcp://192.168.99.103:2376
staging   *        digitalocean   Running   tcp://203.0.113.81:2376

If you check:

$ echo $DOCKER_HOST
tcp://203.0.113.81:2376  ====> it will point to staging

All you have to do now is (tried on Docker terminal):

$ DOCKER_HOST=tcp://192.168.99.103:2376

And now if you check:

$ docker-machine ls

NAME      ACTIVE   DRIVER         STATE     URL
dev       *        virtualbox     Running   tcp://192.168.99.103:2376
staging   -        digitalocean   Running   tcp://203.0.113.81:2376

The active container has moved to 'dev'!! From now on all your commands like 'docker container ls' etc. should reflect your newly active container.

But please note this arrangement will work only for the Docker terminal where you changed the default container i.e. if you close and re-open a new terminal or open another Docker terminal the original default container (staging in this example) will be active.