[Feature] Support other container image registries, including private ones

[alexellis]

Description

Support other container image registries, including private ones

Detail

• Users should be able to deploy public images stored outside of the Docker Hub in third-party registries such as GitLab's public registry or quay.io
• Private images which require authentication to be pulled should also be supported, whether stored on the Docker Hub or a third-party registry

Context

Today faasd only has support for images on the docker.io/ public registry. Other backends for OpenFaaS support this feature including faas-netes and faas-swarm.

[KaiWedekind]

Thank you Alex!

[alexellis]

@KaiWedekind are your repos public and without auth, just not on docker.io, or are they also private? We have two use-cases and I’d like to support it in two steps.

[KaiWedekind]

@alexellis I'm am using a self hosted GitLab and their container registry. My repos there are private.

I was using this line in my .gitlab-ci.yaml to login. Ref

- echo -n "$CI_DOCKER_LOGIN" | docker login --username admin --password-stdin registry.<HOST>.io

Build and push to the container registry works, it is just the deployment.
Thank you, Alex.

[estesp]

Some help on using the Go API to support authenticated registry interactions:

When used as a CRI provider, the CRI plugin has its own configuration for registry auth: https://github.com/containerd/cri/blob/master/docs/registry.md

When using the Go client API for containerd, you can see from the ctr images pull implementation (as one example) how it sets up the NewDockerAuthorizer using these helper functions: https://github.com/containerd/containerd/blob/master/cmd/ctr/commands/resolver.go

[alexellis]

I suspect that a nice experience might be to have users copy their .docker/config.json file to a known location, and for the faasd daemon to always use that to resolve images. A good location may be: /var/lib/faasd/.docker/config.json

The Docker config JSON file is also used in Kubernetes and can support multiple remotes.

[alexellis]

Thank you @estesp

[alexellis]

Added to Trello roadmap for 2020.

[AkihiroSuda]

PR #41

[alexellis]

Many thanks @AkihiroSuda

[alexellis]

@KaiWedekind PTAL :)