Building Cross Platform Docker

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Building Cross Platform Docker

Building Cross Platform Docker

By default, docker build creates images for the architecture that only matches host machine. with the evolution of ARM based architecture, it would be good if single docker images support different platforms such as X86/ARM/AMD.

In order to achieve this we will use the docker BuildX command.

BuildX is a Docker CLI plugin for extended build capabilities with BuildKit.

By default, a build executed with Buildx will build an image for the architecture that matches your machine. This way, you get an image that runs on the same machine you are working on. In order to build for a different architecture, you can set the --platform flag, e.g. --platform=linux/arm64.

How to verify if BuildX already installed

To verify if the BuildX plugin already installed run below command

verifyBuildX.sh
$ ls -lart /usr/libexec/docker/cli-plugins/

-rwxr-xr-x 1 tvajjala tvajjala 8262689 May 7  2023 docker-buildx

Enable buildX support using below attribute in ~/.docker/config.json and restart the docker service.

enable.sh
# Create / Update config.json

$ vi ~/.docker/config.json
{
   "experimental": "enabled"
}

# Restart
$ systemctl restart docker

# Verify
$ docker buildx version

Supported platforms

To verify if your docker image support multiplatform run below command

XPlatformDocker.sh
docker buildx imagetools inspect codergists/tvajjala
Name:      docker.io/codergists/tvajjala:latest
MediaType: application/vnd.docker.distribution.manifest.list.v2+json
Digest:    sha256:21a3deaa0d32a8057914f36584b5288d2e5ecc984380bc0118285c70fa8c9300

Manifests:
  Name:      docker.io/codergists/tvajjala:latest@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/amd64

  Name:      docker.io/codergists/tvajjalae:latest@sha256:e047bc2af17934d38c5a7fa9f46d443f1de3a7675546402592ef805cfa929f9d
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm/v6

  Name:      docker.io/codergists/tvajjala:latest@sha256:8483ecd016885d8dba70426fda133c30466f661bb041490d525658f1aac73822
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm/v7

  Name:      docker.io/codergists/tvajjala:latest@sha256:c74f1b1166784193ea6c8f9440263b9be6cae07dfe35e32a5df7a31358ac2060
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/arm64/v8

  Name:      docker.io/codergists/tvajjala:latest@sha256:2689e157117d2da668ad4699549e55eba1ceb79cb7862368b30919f0488213f4
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/386

  Name:      docker.io/codergists/tvajjala:latest@sha256:2042a492bcdd847a01cd7f119cd48caa180da696ed2aedd085001a78664407d6
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/ppc64le

  Name:      docker.io/codergists/tvajjala:latest@sha256:49e322ab6690e73a4909f787bcbdb873631264ff4a108cddfd9f9c249ba1d58e
  MediaType: application/vnd.docker.distribution.manifest.v2+json
  Platform:  linux/s390x
manifestInspect.sh
sudo docker manifest inspect --verbose codergists/tvajjala

Tools required to build XPlatform Images

Following software required to build

  1. BuildX cli plugin

  2. Moby/builtKit Engine.

  3. QEMU Emulator

  4. Drivers (Ex: container-driver)

BuildX CLI Plugin

BuildX is a Docker CLI plugin for extended build capabilities with BuildKit.

Read more at https://github.com/docker/buildx.

Moby/BuildKit Engine

Docker BuildKit is the next generation container image builder, which helps us to make Docker images more efficient, secure, and faster. It’s integrated into the Docker release version v18.06. but it is downloaded as separate docker image during builder instance creation.

QEMU Emulator

QEMU is a free and open-source emulator. It emulates the machine’s processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it to run a variety of guest operating systems.

Below command shows what emulators installed for each of the builders.

listEmulators.sh
docker buildx ls

If you don’t see them listed for your system you can install them with the tonistiigi/binfmt image.

emulatorInstall.sh
$ docker run --privileged --rm tonistiigi/binfmt --install all

BuildX Drivers

The buildX client connects out to the BuildKit backend to execute builds. BuildX drivers allow fine-grained control over management of the backend, and supports different options for where and how BuildKit should run.

It supports following drivers.

  • The docker driver, that uses the BuildKit library bundled into the Docker daemon

  • The docker-container driver, that launches a dedicated BuildKit container using Docker, for access to advanced features like multi-platform builds.

  • The kubernetes driver, that launches dedicated BuildKit pods in a remote Kubernetes cluster, for scalable builds

  • The remote driver, that allows directly connecting to a manually managed BuildKit daemon, for more custom setups.

multi-platform images only supported when using BuildKit with docker-container driver.

Builder Instance

In order to build multi-platform images, we also need to create a builder instance(isolate environment) as building multi-platform images currently only supported when using BuildKit with docker-container driver.

Builder instances is an isolated environment where builds can be invoked.

Below command create builder instance with name cross-platform-build and make it default builder instance also bootstraps.

buildInstance.sh
# Syntax
$ docker buildx create --name=<builder-name> --driver=<driver> --driver-opt=<driver-options>

# Create and change it to default
$ docker buildx create --name cross-platform-build --driver docker-container --use

# Bootstrap
$ docker buildx inspect --bootstrap

# Verify
$ docker buildx ls

Publish to Repository

Default, image build with BuildX resides inside emulator. they are not visible on parentVM.

Two ways we can push to docker repository.

  • push - It directly pushes to remote repository (Recommended).

  • load - It loads back from emulator to parent VM docker engine. so that it will display created image on VM when you run docker images command.

Push to repository.

you can push mutiple images(with different platforms) at once.
image tag name shouldn’t have forward slashes.
buildPush.sh
docker buildx build --push  --platform linux/amd64,linux/arm64 -t <registry-base-url>/<image>:latest .

Load docker image to parent VM

--load only supports one platform value. You need to push separately to docker registry
buildLoad.sh
docker buildx build --load --platform linux/amd64 -t <image>:latest .

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