Multi-platform builds with Gitlab CI (part 2)

After using a M1 Mac Mini for a while, I upgraded my personal laptop to a M1 Max 14” MacBook Pro, and I’ve started using 64-bit ARM containers on AWS, Oracle Cloud, and Hetzner’s cloud service.

Previously, I used Docker Buildx and QEMU to build arm64 containers, but this is really slow - so I went looking at options to build natively.

GitLab CI provide an arm64 runner build, and Oracle Cloud have an “Always Free” Ampere option - with up to 24GB of RAM and up to 4 VCPUs.

This is how I set it up.

Preparing the x86_64 runner

Install an OS on your runner. This is a VM on my own hardware, so I went with Debian.
Install up to date Docker. Follow the official instructions.
Install the Gitlab CI runner. Follow the official instructions.
Register your runner. Follow the official instructions. Give it a unique tag - I used amd64.

Add some default environment variables to /etc/gitlab-runner/config.toml:

concurrent = 1
check_interval = 0
shutdown_timeout = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "x86_64 runner"
  url = *snip*
  id = *snip*
  token = *snip*
  token_obtained_at = *snip*
  token_expires_at = *snip*
  executor = "docker"
  [runners.cache]
    MaxUploadedArchiveSize = 0
  [runners.docker]
    tls_verify = false
    image = "docker:stable"
    privileged = true
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/certs/client", "/cache"]
    shm_size = 0

Restart the gitlab runner:
```
systemctl restart gitlab-runner
```

Preparing the arm64 runner

Install an OS on your runner. Oracle limit their free service to Oracle Linux or Ubuntu, so I went with Ubuntu.
Install up to date Docker. Follow the official instructions.
Install the Gitlab CI runner. Follow the official instructions.
Register your runner. Follow the official instructions. Give it a unique tag - I used arm64.

Add some default environment variables to /etc/gitlab-runner/config.toml:

concurrent = 1
check_interval = 0
shutdown_timeout = 0

[session_server]
  session_timeout = 1800

[[runners]]
  name = "ARM64 OCI runner"
  url = *snip*
  id = *snip*
  token = *snip*
  token_obtained_at = *snip*
  token_expires_at = *snip*
  executor = "docker"
  [runners.cache]
    MaxUploadedArchiveSize = 0
  [runners.docker]
    tls_verify = false
    image = "docker:stable"
    privileged = true
    disable_entrypoint_overwrite = false
    oom_kill_disable = false
    disable_cache = false
    volumes = ["/certs/client", "/cache"]
    shm_size = 0

Restart the gitlab runner:
```
systemctl restart gitlab-runner
```

Making a multi-platform build

Use a template a bit like:

image: docker:latest

services:
   - docker:dind

before_script:
   - docker login -u $CI_REGISTRY_USER -p $CI_REGISTRY_PASSWORD $CI_REGISTRY

amd64-docker-build-latest:
   stage: build
   tags:
      - amd64
   script:
      - docker build -t "$CI_REGISTRY_IMAGE:latest-amd64" .
      - docker push "$CI_REGISTRY_IMAGE:latest-amd64"
   only:
      - master
      - main

arm64-docker-build-latest:
   stage: build
   tags:
      - arm64
   script:
      - docker build -t "$CI_REGISTRY_IMAGE:latest-arm64" .
      - docker push "$CI_REGISTRY_IMAGE:latest-arm64"
   only:
      - master
      - main

manifest-docker-build-latest:
   stage: deploy
   script:
      - docker manifest create "$CI_REGISTRY_IMAGE:latest" "$CI_REGISTRY_IMAGE:latest-amd64" "$CI_REGISTRY_IMAGE:latest-arm64"
      - docker manifest push "$CI_REGISTRY_IMAGE:latest"
   only:
      - master
      - main

amd64-docker-build:
   stage: build
   tags:
      - amd64
   script:
      - docker build -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-amd64" .
      - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-amd64"
   except:
      - master
      - main

arm64-docker-build:
   stage: build
   tags:
      - arm64
   script:
      - docker build -t "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-arm64" .
      - docker push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-arm64"
   except:
      - master
      - main

manifest-docker-build:
   stage: deploy
   script:
      - docker manifest create "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG" "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-amd64" "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG-arm64"
      - docker manifest push "$CI_REGISTRY_IMAGE:$CI_COMMIT_REF_SLUG"
   except:
      - master
      - main

At this point, you should have a working multi-platform image!