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Ajeet Raina Docker Captain, ARM Innovator & Docker Bangalore Community Leader.

How I built ARM based Docker Images for Raspberry Pi using buildx CLI Plugin on Docker Desktop?

10 min read

2 weeks back in Dockercon 2019 San Francisco, Docker & ARM demonstrated the integration of ARM capabilities into Docker Desktop Community for the first time. Docker & ARM unveiled go-to-market strategy to accelerate Cloud, Edge & IoT Development. These two companies have planned to streamline the app development tools for cloud, edge, and internet of things environments built on ARM platform. The tools include AWS EC2 A1 instances based on AWS’ Graviton Processors (which feature 64-bit Arm Neoverse cores). Docker in collaboration with ARM will make new Docker-based solutions available to the Arm ecosystem as an extension of Arm’s server-tailored Neoverse platform, which they say will let developers more easily leverage containers — both remote and on-premises which is going to be pretty cool.

This integration is today available to the approximately 2 million developers using Docker Desktop Community Edition . As part of Docker Captain’s programme, we were lucky to get an early access to this build during Docker Captain Summit which took place on the first day of Dockercon 2019.

Introducing buildx

Under Docker 19.03.0 Beta 3, there is a new experimental CLI plugin called “buildx”. It is a pretty new Docker CLI plugin that extends the docker build command with the full support of the features provided by Moby BuildKit builder toolkit. It provides the same user experience as docker build with many new features like creating scoped builder instances and building against multiple nodes concurrently. As per the discussion with Docker staff, the “x” under buildx might get dropped in near future and features and flags are too subjected to change when the stable release is announced.

Buildx always build using the BuildKit engine and does not require DOCKER_BUILDKIT=1 environment variable for starting builds. Buildx build command supports the features available for docker build including the new features in Docker 19.03 such as outputs configuration, inline build caching or specifying target platform. In addition, buildx supports new features not yet available for regular docker build like building manifest lists, distributed caching, exporting build results to OCI image tarballs etc.

How does builder Instance work?

Buildx allows you to create new instances of isolated builders. This can be used for getting a scoped environment for your CI builds that does not change the state of the shared daemon or for isolating the builds for different projects. You can create a new instance for a set of remote nodes, forming a build farm, and quickly switch between them.

New instances can be created with docker buildx create command. This will create a new builder instance with a single node based on your current configuration. To use a remote node you can specify the DOCKER_HOST or remote context name while creating the new builder. After creating a new instance you can manage its lifecycle with the inspectstop and rm commands and list all available builders with ls. After creating a new builder you can also append new nodes to it.

To switch between different builders use docker buildx use <name>. After running this command the build commands would automatically keep using this builder.

Docker 19.03 also features a new docker context command that can be used for giving names for remote Docker API endpoints. Buildx integrates with docker context so that all of your contexts automatically get a default builder instance. While creating a new builder instance or when adding a node to it you can also set the context name as the target.

Enough theory !!! Do you really want to see it in action? Under this blog post, I will showcase how I built ARM-based Docker Images for my tiny Raspberry cluster using `docker buildx’ utility which runs on my Docker Desktop for Mac.

Installing Docker Desktop for Mac

Open up for an early access of Docker Desktop. Do switch to Edge release if in case you’ve installed stable version of Docker Desktop.

As of today, Docker Desktop Edge Community Edition comes with Engine 19.03.0 Beta 3, latest Kubernetes v1.1.4.1 and Compose 1.24.0 Release.

Verifying the docker buildx CLI

[Captains-Bay]? >  docker buildx --help

Usage:	docker buildx COMMAND

Build with BuildKit

Management Commands:
  imagetools  Commands to work on images in registry

  bake        Build from a file
  build       Start a build
  create      Create a new builder instance
  inspect     Inspect current builder instance
  ls          List builder instances
  rm          Remove a builder instance
  stop        Stop builder instance
  use         Set the current builder instance
  version     Show buildx version information 

Run 'docker buildx COMMAND --help' for more information on a command.

Listing all builder instances and the nodes for each instance

[Captains-Bay]? >  docker buildx ls
default * docker                  
  default default         running linux/amd64, linux/arm64, linux/arm/v7, linux/arm/v6

We are currently using the default builder, which is basically the old builder.

Creating a New Builder Instance

The `docker buildx create` makes a new builder instance pointing to a docker context or endpoint, where context is the name of a context from docker context ls and endpoint is the address for docker socket (eg. DOCKER_HOST value).

By default, the current docker configuration is used for determining the context/endpoint value.

Builder instances are isolated environments where builds can be invoked. All docker contexts also get the default builder instance.

Let’s create a new builder, which gives us access to some new multi-arch features.

[Captains-Bay]? >  docker buildx create --help

Usage:	docker buildx create [OPTIONS] [CONTEXT|ENDPOINT]

Create a new builder instance

      --append                 Append a node to builder instead of changing it
      --driver string          Driver to use (eg. docker-container)
      --leave                  Remove a node from builder instead of changing it
      --name string            Builder instance name
      --node string            Create/modify node with given name
      --platform stringArray   Fixed platforms for current node
      --use                    Set the current builder instance

Creating a new builder called “testbuilder”

[Captains-Bay]? >  docker buildx create --name testbuilder
[Captains-Bay]? >  docker buildx ls
testbuilder    docker-container                     
  testbuilder0 unix:///var/run/docker.sock inactive 
default *      docker                               
  default      default                     running  linux/amd64, linux/arm64, linux/arm/v7, linux/arm/v6
[Captains-Bay]? > 

Switching to “testbuilder” builder instance

[Captains-Bay]? >  docker buildx use testbuilder
[Captains-Bay]? >  docker buildx ls
testbuilder *  docker-container                     
  testbuilder0 unix:///var/run/docker.sock inactive 
default        docker                               
  default      default                     running  linux/amd64, linux/arm64, linux/arm/v7, linux/arm/v6
[Captains-Bay]? > 

Here I created a new builder instance with the name mybuilder, switched to it, and inspected it. Note that –bootstrap isn’t needed, it just starts the build container immediately. Next we will test the workflow, making sure we can build, push, and run multi-arch images.

What is –bootstrap all about?

The `docker buildx inspect –bootstrap ensures that the builder is running before inspecting it. If the driver is docker-container, then --bootstrap starts the buildkit container and waits until it is operational. Bootstrapping is automatically done during build, it is thus not necessary. The same BuildKit container is used during the lifetime of the associated builder node (as displayed in buildx ls).

[Captains-Bay]? >  docker buildx inspect --bootstrap
[+] Building 22.4s (1/1) FINISHED                                                                                        
 => [internal] booting buildkit                                                                                    22.4s
 => => pulling image moby/buildkit:master                                                                          21.5s
 => => creating container buildx_buildkit_testbuilder0                                                              0.9s
Name:   testbuilder
Driver: docker-container

Name:      testbuilder0
Endpoint:  unix:///var/run/docker.sock
Status:    running
Platforms: linux/amd64, linux/arm64, linux/arm/v7, linux/arm/v6
[Captains-Bay]? >  

Authenticating with Dockerhub

[Captains-Bay]? >  docker login
Login with your Docker ID to push and pull images from Docker Hub. If you don't have a Docker ID, head over to to create one.
Username: ajeetraina
Login Succeeded

Cloning the Repository

[Captains-Bay]? >  git clone
Cloning into 'docker-cctv-raspbian'...
remote: Enumerating objects: 47, done.
remote: Counting objects: 100% (47/47), done.
remote: Compressing objects: 100% (31/31), done.
remote: Total 47 (delta 20), reused 32 (delta 14), pack-reused 0
Unpacking objects: 100% (47/47), done.

Peeping into Dockerfile

[Captains-Bay]? >  cat Dockerfile 
FROM resin/rpi-raspbian:latest

RUN apt update && apt upgrade && apt install motion
RUN mkdir /mnt/motion && chown motion /mnt/motion
COPY motion.conf /etc/motion/motion.conf

VOLUME /mnt/motion
ENTRYPOINT ["motion"]
[Captains-Bay]? >

Building ARM-based Docker Image

[Captains-Bay]? >  docker buildx build --platform linux/amd64,linux/arm64,linux/arm/v7 -t ajeetraina/docker-cctv-raspbian --push .

[Captains-Bay]? >  docker buildx build --platform linux/amd64,linux/arm64,linux/arm/v7 -t ajeetraina/docker-cctv-raspbian --push .
[+] Building 254.2s (12/21)                                                                                              
[+] Building 2174.9s (22/22) FINISHED                                                                                    
 => [internal] load build definition from Dockerfile                                                                0.1s
 => => transferring dockerfile: 268B                                                                                0.0s
 => [internal] load .dockerignore                                                                                   0.1s
 => => transferring context: 2B                                                                                     0.0s
 => [linux/arm/v7 internal] load metadata for                                   8.8s
 => [linux/arm64 internal] load metadata for                                    8.8s
 => [linux/amd64 internal] load metadata for                                    8.8s
 => [linux/amd64 1/4] FROM  0.1s
 => => resolve  0.0s
 => [internal] load build context                                                                                   0.1s
 => => transferring context: 27.72kB                                                                                0.0s
 => [linux/arm64 1/4] FROM  17.3s
 => => resolve  0.0s
 => => sha256:18be79e066099cce5c676f7733a6ccb4733ed5962a996424ba8a15d5f88d055b 2.81kB / 2.81kB                      0.0s
 => => sha256:67a3f53689ffd00b59f9a7b7f8af0da5b36c9e11e12ba43b35969586e0121303 1.56kB / 1.56kB                      2.3s
 => => sha256:ef16d706debb7a56d89bf14958aca2da76bd3d0a42a6762c37302c9527a47d10 305B / 305B                          3.5s
 => => sha256:2734b459704280a5238405384487095392e5414d973554b27545cec0e984a0f2 256B / 256B                          3.1s
 => => sha256:9d5b46a00008070b009b685af5846c225ad170f38768416b63917ea7ac94062d 7.75kB / 7.75kB                      4.4s
 => => sha256:5fb2b6f7daac67a8465e8201c76828550b811619be473ab594972da35b4b7ee7 354B / 354B                          4.4s
 => => sha256:a04aef7b1e2fc4905fea2a685c63bc1eeb94c86149fd1286459206c22794e610 177B / 177B                          4.4s
 => => sha256:3eae71a21b9db8bd54d6a189b7587a10f52d6ffee3d868705a89974fe574c268 234B / 234B                          2.3s
 => => sha256:28f1ee4d4d5aa8bb96b3ba6a5e2177b2b58b595edaf601b9aae69fd02f78a6c6 7.48kB / 7.48kB                      0.0s
 => => sha256:6bddb275e70b0083d76083d01be2c3da11f67f526a123adcc980c5a3260d46e8 51.54MB / 51.54MB                   13.4s
 => => sha256:873755612f304f066db70c4015fdeadc9a81c0e6e25fb1aa833aeba80a7aeffc 229B / 229B                          3.9s
 => => sha256:78ba3f0466312c019467b178339a89120f2dce298d7c3d5e6840b3566749f5c0 250B / 250B                          3.2s
 => => sha256:b98db37cf25231afe68852e2cb21fb8aa465bb7a32ecc9afc6dec100ec0ba9b0 367B / 367B                          3.5s
 => => sha256:6b6c68e7ac8567569cee8da92431637e561e7aef5addb70373401d0887447a00 363B / 363B                          4.4s
 => => unpacking  3.8s
 => [linux/arm/v7 1/4] FROM  0.0s
 => => resolve  0.0s
 => [linux/amd64 2/4] RUN cat /.resin/deprecation-warning                                                           0.6s
 => [linux/arm/v7 2/4] RUN cat /.resin/deprecation-warning                                                          0.5s
 => [linux/arm64 2/4] RUN cat /.resin/deprecation-warning                                                           0.6s
 => [linux/arm/v7 3/4] RUN apt update && apt upgrade && apt install motion                                        481.2s
 => [linux/amd64 3/4] RUN apt update && apt upgrade && apt install motion                                        1431.5s
 => [linux/arm64 3/4] RUN apt update && apt upgrade && apt install motion                                        1665.5s
 => [linux/arm/v7 4/4] RUN mkdir /mnt/motion && chown motion /mnt/motion                                            0.6s
 => [linux/arm/v7 5/4] COPY motion.conf /etc/motion/motion.conf                                                     0.1s
 => [linux/amd64 4/4] RUN mkdir /mnt/motion && chown motion /mnt/motion                                             0.6s
 => [linux/amd64 5/4] COPY motion.conf /etc/motion/motion.conf                                                      0.1s
 => [linux/arm64 4/4] RUN mkdir /mnt/motion && chown motion /mnt/motion                                             0.6s
 => [linux/arm64 5/4] COPY motion.conf /etc/motion/motion.conf                                                      0.1s
 => exporting to image                                                                                            481.7s
 => => exporting layers                                                                                            19.6s
 => => exporting manifest sha256:55ddd5c67557190344efea7327a5b2f8de0bdc8ba184f856b1086baac6bed702                   0.0s
 => => exporting config sha256:ebb6e951b8f206d258e8552313633c35f4fe4c82fe7a7fcc51475022ae089c2d                     0.0s
 => => exporting manifest sha256:7b6919de7edd7d1be695877f827e7ee6d302d3acfd3f69ed73bf2ffaa4a80632                   0.0s
 => => exporting config sha256:a83b02bf9cbcb408110c4b773f4e5edde04f35851e2a42d4ff1d947c132bed6d                     0.0s
 => => exporting manifest sha256:d379c0f79b6a72a770124bb2ee94d91d9afef031c81ac20ea7a4c51f4f13ddf2                   0.0s
 => => exporting config sha256:86c2e637fe39036d51779c3bb5f800d3e8da14122907c5fd03bdace47b03bb38                     0.0s
 => => exporting manifest list sha256:daec2787002024c07addf56a8099a866d7f1cd85ed8c33818beb64a5a208cd54              0.0s
 => => pushing layers                                                                                             455.4s
 => => pushing manifest for                                        6.4s

Awesome. It worked ! The –platform flag enabled buildx to generate Linux images for Intel 64-bit, Arm 32-bit, and Arm 64-bit architectures. The –push flag generates a multi-arch manifest and pushes all the images to Docker Hub. Cool, isn’t it?

What is this ImageTools all about?

Imagetools contains commands for working with manifest lists in the registry. These commands are useful for inspecting multi-platform build results. It creates a new manifest list based on source manifests. The source manifests can be manifest lists or single platform distribution manifests and must already exist in the registry where the new manifest is created. If only one source is specified create performs a carbon copy.

Let’s use imagetools to inspect what we did.

[Captains-Bay]? >  docker buildx imagetools inspect
MediaType: application/vnd.docker.distribution.manifest.list.v2+json
Digest:    sha256:daec2787002024c07addf56a8099a866d7f1cd85ed8c33818beb64a5a208cd54
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/amd64
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm64
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm/v7
[Captains-Bay]? >

The image is now available on Docker Hub with the tag ajeetraina/docker-cctv-raspbian:latest. You can run a container from that image on Intel laptops, Amazon EC2 A1 instances, Raspberry Pis, and more. Docker pulls the correct image for the current architecture, so Raspberry Pis run the 32-bit Arm version and EC2 A1 instances run 64-bit Arm.

Verifying this Image on Raspberry Pi Node

root@node2:/home/pi# cat /etc/os-release
PRETTY_NAME="Raspbian GNU/Linux 9 (stretch)"
NAME="Raspbian GNU/Linux"
VERSION="9 (stretch)"

Verify the Docker version

root@node2:/home/pi# docker version
 Version:           18.09.0
 API version:       1.39
 Go version:        go1.10.4
 Git commit:        4d60db4
 Built:             Wed Nov  7 00:57:21 2018
 OS/Arch:           linux/arm
 Experimental:      false

Server: Docker Engine - Community
  Version:          18.09.0
  API version:      1.39 (minimum version 1.12)
  Go version:       go1.10.4
  Git commit:       4d60db4
  Built:            Wed Nov  7 00:17:57 2018
  OS/Arch:          linux/arm
  Experimental:     false

Running the Docker Image

root@node2:/home/pi# docker pull ajeetraina/docker-cctv-raspbian:latest
latest: Pulling from ajeetraina/docker-cctv-raspbian
6bddb275e70b: Already exists
ef16d706debb: Already exists
2734b4597042: Already exists
873755612f30: Already exists
67a3f53689ff: Already exists
5fb2b6f7daac: Already exists
a04aef7b1e2f: Already exists
9d5b46a00008: Already exists
b98db37cf252: Already exists
78ba3f046631: Already exists
6b6c68e7ac85: Already exists
3eae71a21b9d: Already exists
db08b1848bc3: Pull complete
9c84b2387994: Pull complete
3579f37869a5: Pull complete
Digest: sha256:daec2787002024c07addf56a8099a866d7f1cd85ed8c33818beb64a5a208cd54
Status: Downloaded newer image for ajeetraina/docker-cctv-raspbian:latest

Inspecting the Docker Image

 docker image inspect ajeetraina/docker-cctv-raspbian:latest | grep arm
        "Architecture": "arm",

Running the Docker Container

 docker run -dit -p 8000:8000 ajeetraina/docker-cctv-raspbian:latest
root@node2:/home/pi# docker ps
CONTAINER ID        IMAGE                                    COMMAND             CREATED             STATUS              PORTS                              NAMES
c43f25cd0667        ajeetraina/docker-cctv-raspbian:latest   "motion"            7 seconds ago       Up 2 seconds>8000/tcp, 8081/tcp   zen_brown

Verifying the Logs

root@node2:/home/pi# docker logs -f c43
[0] [NTC] [ALL] conf_load: Processing thread 0 - config file /etc/motion/motion.conf
[0] [NTC] [ALL] motion_startup: Motion 3.2.12+git20140228 Started
[0] [NTC] [ALL] motion_startup: Logging to syslog
[0] [NTC] [ALL] motion_startup: Using log type (ALL) log level (NTC)
[0] [NTC] [ENC] ffmpeg_init: ffmpeg LIBAVCODEC_BUILD 3670016 LIBAVFORMAT_BUILD 3670272
[0] [NTC] [ALL] main: Thread 1 is from /etc/motion/motion.conf
[0] [NTC] [ALL] main: Thread 1 is device: /dev/video0 input -1
[0] [NTC] [ALL] main: Stream port 8081
[0] [NTC] [ALL] main: Waiting for threads to finish, pid: 1
[1] [NTC] [ALL] motion_init: Thread 1 started , motion detection Enabled
[1] [NTC] [VID] vid_v4lx_start: Using videodevice /dev/video0 and input -1
[1] [ALR] [VID] vid_v4lx_start: Failed to open video device /dev/video0:
[1] [WRN] [ALL] motion_init: Could not fetch initial image from camera Motion continues using width and height from config file(s)
[1] [NTC] [ALL] image_ring_resize: Resizing pre_capture buffer to 1 items
[1] [NTC] [STR] http_bindsock: motion-stream testing : IPV4 addr: port: 8081
[1] [NTC] [STR] http_bindsock: motion-stream Bound : IPV4 addr: port: 8081
[1] [NTC] [ALL] motion_init: Started motion-stream server in port 8081 auth Disabled
[1] [NTC] [ALL] image_ring_resize: Resizing pre_capture buffer to 3 items
[0] [NTC] [STR] httpd_run: motion-httpd testing : IPV4 addr: port: 8080
[0] [NTC] [STR] httpd_run: motion-httpd Bound : IPV4 addr: port: 8080
[0] [NTC] [STR] httpd_run: motion-httpd/3.2.12+git20140228 running, accepting connections
[0] [NTC] [STR] httpd_run: motion-httpd: waiting for data on port TCP 8080

Hence, it is now so easy to build ARM-based Docker Images on your Docker Desktop and then share it to DockerHub so that anyone can pull this image on their Raspberry Pi and run it flawlessly.


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Ajeet Raina Docker Captain, ARM Innovator & Docker Bangalore Community Leader.

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