GoReleaser and Docker Manifests¶
Let's see how to create Docker manifests with GoReleaser.
Question:¶
Did you know, that you can create Docker Manifest Layer with GoReleaser?
No?¶
In this article we will see what Docker Manifests are and how can use them in GoReleaser to delivery multi-arch builds under one single tag.
But let us start, with the idea behind Docker Image Manifest.
What are Docker Image Manifests?¶
A Docker manifests describe all the layers inside an image. And with the help of the manifest we can exact compare two images, independent from their actual human-readable tag.
Manifests are expressed in JSON and contain all the information about the different image layers and the architectures.
Docker uses then the manifests to work out if an image is compatible with the current device architecture. And then uses this particular informations to determine on how to start new containers.
Currently the manifest schema is at version 2.
A manifest file will declare its schema version and then a list of manifest entries available for the image. The entries will then point to a different variation of the image, such as amd64 and arm64.
You can easily view the image manifest using the docker manifest inspect command.
This works fine with local images or images stored in a remote registry.
docker manifest inspect <image>:<version>
Example output of the docker manifest inspect command
Multi-Arch Builds and Manifests¶
For a long time Docker did not support multiple image architectures. You could only run images with the same architecture as they where build for. With the rise of ARM-based machines this was really a limiting factor.
But with manifests, developers can now support multiple architectures under one single image tag. The Docker client itself picks the underlying image version for its particular platform. Great and simple!
Keep in mind: There should be no changes, other the target architecture or operating system in the images. Do not deliver images with completely different functionality under the same tag.
You can read more about docker manifests here: https://docs.docker.com/engine/reference/commandline/manifest/
On side note: docker manifest is still an experimental feature and needs to be activated in your Docker client.
GoReleaser¶
Now that you know what Docker manifest are, we can give GoReleaser the task of the heavy lifting and let it create the Docker manifest as part of our release process.
All you need to do is to add the docker_manifests to your .goreleaser.yaml. The most important part is to map name_template to the image_templates you created in the dockers step.
Example snippet of a
.gorelaser.yaml
There are some additional flags you can set, e.g. if you have a self-hosted Docker registry with self-signed certificates, you can pass the insecure flag.
Check out the official GoReleaser documentation https://goreleaser.com/customization/docker_manifest/ for an in-depth overview.
Summary¶
With GoReleaser its a breeze to create Docker manifest for your multi arch builds. Go try it out!
