What is the relationship between running a docker container and creating a docker machine?

My assumption was that when you use docker run and image is taken and turned into a running container. That container is running on a virtual machine that was created by docker-machine create. However I can create containers using docker run without having ever created a docker machine.

I am asking because I am trying to follow a tutorial where the presenter runs a process that is accepting information on a port. He executes:

docker run --rm -ti -p 45678:45678 -p 45679:45679 --name echo-server ubuntu:14.04 bash

then inside the container:

nc -lp 45678 | nc -lp 45679

Then in a different terminal he uses docker-machine ip and recieves and ip address (later on he creates another container to relay the output to, but i didn’t get that far). However I just get “Error: No machine name(s) specified and no “default” machine exists”.

I see that I can create a machine using virtualbox or whatever other software, but how is that related to the container I just created? How am I running this container with no machine? Is there a hidden machine that I am running it on or are there multiple ways to run containers? If there is no machine, how do I get the IP address of the container?

Thanks, just getting started with this stuff, hope this is the right area to ask this question.

Are you using “Docker for Mac” or “Docker Toolbox”? Is there a whale icon on your menu bar?

The not-toolbox “Docker for Mac” product tries hard to hide the VM (it is there in reality, but it’s tricky to get at) and it doesn’t interact with docker-machine at all. When you run

you can access those published ports from the host on the localhost IPv4 address

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Ah, using worked, thanks!

There is a whale icon in the menu bar. I assume that means that I’m using Docker for Mac then correct?

Would that mean I won’t be using docker-machine for anything? And I can just pretend that there is no virtual machine and assume everything is running on my local IP as if I was using Docker on Linux?

Does this limit any functionalities that were previously available with docker machine? Is there any reason I won’t want to use docker-machine for anything?


…that’s the theory…

A quick glance through the forum should find you much longer threads on both of these, but the three big issues I’m aware of:

  • If your workflow depends on bind-mounting (docker run -v) large amounts of data from the host system into the container (like your entire application) you may find Docker for Mac slow and unstable; but if you docker build your application it works fine
  • If your workflow depends on --net=host, whatever you’re expecting from it probably won’t work
  • If your workflow depends on a fixed container-visible IP address for the host, or specific host-visible IP addresses for containers, this won’t work

I tend to actually use docker-machine still, either because (2) our whole-application deployment uses a Consul-based setup that depends on --net=host, or (3) a test framework assumes that there exists a single IP address that both the host and all of the containers can use to reach the containers ( on Linux, on Machine) and it just isn’t there.

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Thank you so much for the answer they help a lot with me figuring out where to look for more in depth information. And where to begin my searches.

So there shouldn’t be any issue with just using docker-machine still even though I have Docker for Mac? I can create a docker-machine using virtualbox still and would be able to more accurately follow along with most tutorials I see?

A last question would be, if I was using the Docker Toolbox, would that mean that the docker machine would need to be (visibly) created? Like I would not be able to start a container without there being a docker-machine active? I assume that one is created by default, but it would still need to be there right?

Correct. You can even have both running; eval $(docker-machine env default) will use your Machine VM, and eval $(docker-machine env -u) will switch back to the Docker for Mac version.

You definitely need to manually manage the docker-machine VM if you’re using that path. I don’t totally know what Docker Toolbox does on installation, but a default docker-machine create is pretty straightforward if one isn’t created for you.