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Multi-arch build, what about GitLab CI?

Following the previous article where we saw how to build multi arch images using GitHub Actions, we will now show how to do the same thing using another CI. In this article, we’ll show how to use GitLab CI, which is part of the GitLab.

To start building your image with GitLab CI, you will first need to create a .gitlab-ci.yml file at the root of your repository, commit it and push it.

image: docker:stable

variables:
  DOCKER_HOST: tcp://docker:2375/
  DOCKER_DRIVER: overlay2

services:
  - docker:dind

build:
  stage: build
  script:
    - docker version

This should result in a build output that shows the version of the Docker CLI and Engine: 

We will now install Docker buildx. Because GitLabCI runs everything in containers and uses any image you want to start this container, we can use one with buildx preinstalled, like the one we used for CircleCI. And as for CircleCI, we need to start a builder instance.

image: jdrouet/docker-with-buildx:stable

variables:
  DOCKER_HOST: tcp://docker:2375/
  DOCKER_DRIVER: overlay2

services:
  - docker:dind

build:
  stage: build
  script:
    - docker buildx create --use
    - docker Continue reading

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Multi-arch build, what about Travis?

Following the previous article where we saw how to build multi arch images using GitHub Actions, we will now show how to do the same thing using another CI. In this article, we’ll consider Travis, which is one of the most tricky ones to use for this use case.

To start building your image with Travis, you will first need to create .travis.yml file at the root of your repository.

language: bash
dist: bionic
services:
  - docker
script:
  - docker version

You may notice that we specified using “bionic” to have the latest version of Ubuntu available – Ubuntu 18.04 (Bionic Beaver). As of today (May 2020), if you run this script, you’ll be able to see that the Docker Engine version it provides is 18.06.0-ce which is too old to be able to use buildx. So we’ll have to install Docker manually.

language: bash
dist: bionic
before_install:
  - sudo rm -rf /var/lib/apt/lists/*
  - curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo apt-key add -
  - sudo add-apt-repository "deb [arch=amd64] https://download.docker.com/linux/ubuntu $(lsb_release -cs) edge"
  - sudo apt-get update
  - sudo apt-get -y -o Dpkg::Options::="--force-confnew" install docker-ce
script:
Continue reading

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Multi-arch build, what about CircleCI?

Following the previous article where we saw how to build multi arch images using GitHub Actions, we will now show how to do the same thing using another CI. In this article, we’ll consider CircleCI, which is one of the most used CI SaaS.

To start building your image with CircleCI, you will first need to create .circleci/config.yml file:

version: 2
jobs:
  build:
    docker:
      - image: docker:stable
    steps:
      - checkout
      - setup_remote_docker:
          version: 18.09.3
      - run: docker version

You may notice that we specified using version 18.09.3 of the Docker Engine because buildx requires version 18.09 or later but CircleCI doesn’t provide any version above 18.09.3.

At this point we are able to interact with the Docker CLI but we don’t yet have the buildx plugin installed. To install it, we will download a build from GitHub.

version: 2
jobs:
  build:
    docker:
      - image: docker:stable
    steps:
      - checkout
      - setup_remote_docker:
          version: 18.09.3
Continue reading

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Multi-arch build and images, the simple way

“Build once, deploy anywhere” is really nice on the paper but if you want to use ARM targets to reduce your bill, such as Raspberry Pis and AWS A1 instances, or even keep using your old i386 servers, deploying everywhere can become a tricky problem as you need to build your software for these platforms. To fix this problem, Docker introduced the principle of multi-arch builds and we’ll see how to use this  and put it into production.

Quick setup

To be able to use the docker manifest command, you’ll have to enable the experimental features.

On macOS and Windows, it’s really simple. Open the Preferences > Command Line panel and just enable the experimental features.

On Linux, you’ll have to edit ~/.docker/config.json and restart the engine.

Under the hood

OK, now we understand why multi-arch images are interesting, but how do we produce them? How do they  work?

Each Docker image is represented by a manifest. A manifest is a JSON file containing all the information about a Docker image. This includes references to each of its layers, their corresponding sizes, the hash of the image, its size and also the platform it’s supposed to work on. Continue reading