Support private repo

[AkihiroSuda]

Description

Support private repo with the credential located as /var/lib/faasd/.docker/config.json.

Motivation and Context

#30

• I have Alex has raised an issue to propose this change this is required

How Has This Been Tested?

Tested using a private Docker Hub repo.

$ docker tag functions/figlet:0.13.0 *******/*******:********
$ docker push *******/*******:********
$ faas-cli deploy --image=*******/*******:******** --name=figlet
$ echo hi | faas-cli invoke figlet

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

Commits:

• I've read the CONTRIBUTION guide
• My commit message has a body and describe how this was tested and why it is required.
• I have signed-off my commits with git commit -s for the Developer Certificate of Origin (DCO)

Code:

• My code follows the code style of this project.
• I have added tests to cover my changes.

Docs:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[alexellis]

When I looked at the containerd resolve it seemed cleaner / more lightweight without depending on Docker itself, like this - https://github.com/containerd/containerd/blob/master/cmd/ctr/commands/resolver.go

Do you think it can be made to work without the Docker CLI?

[alexellis]

like "github.com/containerd/containerd/remotes/docker" using NewDockerAuthorizer?

Even it (https://github.com/containerd/containerd/blob/4f348c5b5b53a70b282ab5b81b2cc8f03bf6a338/remotes/docker/authorizer.go#L90) didn't seem to use Docker itself.

What do you think?

[AkihiroSuda]

We can't easily remove dependency on docker/cli, mostly because I believe we want to support cred helper binaries, though I think I've heard that there is an alternative go pkg for that.

[AkihiroSuda]

Maybe we should open docker/cli PR to reduce dependencies

[alexellis]

Is this needed to support the helper binaries then? Does containerd/cri not support pulling from AWS ECR then?

[AkihiroSuda]

https://medium.com/@xynova/keeping-aws-registry-pull-credentials-fresh-in-kubernetes-2d123f581ca6

[alexellis]

I wonder what @ibuildthecloud did in k3c? https://github.com/rancher/k3c/blob/master/pkg/daemon/image.go

I can see a reference to docker/distribution there actually

[alexellis]

Let's go for it, thank you for this PR 👍 If we find a way to remove Docker for auth later on, it can be changed again.