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Close Encounters of the Third Kind, or Microsoft Windows meets Docker ARM Containers for IoT

Tue, Mar 29, 2016

Running an ARM-based Docker container for IoT applications directly on Microsoft Windows looks like an unbelievable extraterrestrial technology from outer space.

This cannot be true, it must be a fake, right?
Or, is this maybe just a cheap magic trick?

Docker for Windows

Nope, believe me, that’s really true…

Behind the scenes

As I showed in my last blog post about the First Touch Down with Docker for Mac, “Docker for Mac” uses an Alpine Linux VM under the hood with the capability of emulating ARM binaries on Intel CPUs. Because of “Docker for Windows” uses exactly the same Alpine Linux in a Hyper-V virtual machine, this should work on Windows 10, too.

The only problem here is, that the bind-mounting of a single binary doesn’t work right now on Windows. I guess this will be fixed in a later release for sure. But we can easily prepare an ARM-based Docker container to make the magic happen.

We just have to put the QEMU emulator binary into the Docker container, and as long as we place it at the correct path /usr/bin/qemu-arm-static, this should work. The easiest way to include the binary to the correct folder is to create a tar archive and use the ADD command in the Dockerfile.

tar vtf qemu-arm-static.tar
drwxr-xr-x  0 dieter staff       0 Mar 28 18:34 usr/
drwxr-xr-x  0 dieter staff       0 Mar 28 18:34 usr/bin/
-rwxr-xr-x  0 dieter staff 2899840 Mar 28 18:34 usr/bin/qemu-arm-static

Dockerfile

FROM hypriot/rpi-busybox-httpd
ADD qemu-arm-static.tar /

With this easy preparation we’re able to start an ARM-based Docker container on Windows 10 with two steps only.

Step 1: Create the modified Docker image

docker build -t rpi-busybox-httpd .

Step 2: Start the QEMU-enabled Docker container

docker run -d -p 80:80 rpi-busybox-httpd

Here in this screenshot you can see all the necessary steps we need, there is really nothing else to do.

Docker for Windows

Voilà - that was the magic trick which can be applied to almost all ARM-based Docker images to make them run in “Docker for Windows” and “Docker for Mac” even on an Intel-based CPU architecture.

Watch the results

“Docker for Windows” publishes the Docker Engine network with the local network name docker. Thus to access the ARM web server, which is running inside of a Linux container, we just have to point our preferred web browser to http://docker/.

Docker for Windows

Key Takeaways

Are you curious now and want to get in touch with “Docker for Windows” by yourself? Then you should register for the Docker BETA program at https://beta.docker.com.

Please send us your feedback on our Gitter channel or tweet your thoughts and ideas on this project at @HypriotTweets.

Dieter @Quintus23M

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