docker-registry-proxy

TL,DR

A caching proxy for Docker; allows centralised management of registries and their authentication; caches images from any registry.

What?

Created as an evolution and simplification of docker-caching-proxy-multiple-private⁠ using the HTTPS_PROXY mechanism and injected CA root certificates instead of /etc/hosts hacks and --insecure-registry

Main feature is Docker layer/image caching, even from S3, Google Storage, etc. As a bonus it allows for centralized management of Docker registry credentials.

You configure the Docker clients (err... Kubernetes Nodes?) once, and then all configuration is done on the proxy -- for this to work it requires inserting a root CA certificate into system trusted root certs.

Usage

• Run the proxy on a host close to the Docker clients
• Expose port 3128 to the network
• Map volume /docker_mirror_cache for up to 32gb of cached images from all registries
• Map volume /ca, the proxy will store the CA certificate here across restarts
• Env REGISTRIES: space separated list of registries to cache; no need to include Docker Hub, its already there.
• Env AUTH_REGISTRIES: space separated list of hostname:username:password authentication info.
  • hostnames listed here should be listed in the REGISTRIES environment as well, so they can be intercepted.
  • For Docker Hub authentication, hostname should be auth.docker.io, username should NOT be an email, use the regular username.
  • For regular registry auth (HTTP Basic), hostname here should be the same... unless your registry uses a different auth server. This should work for quay.io also, but I have no way to test.
  • For Google Container Registry (GCR), username should be _json_key and the password should be the contents of the service account JSON. Check out GCR docs⁠

docker run --rm --name docker_registry_proxy -it \
       -p 0.0.0.0:3128:3128 \
       -v $(pwd)/docker_mirror_cache:/docker_mirror_cache \
       -v $(pwd)/docker_mirror_certs:/ca \
       -e REGISTRIES="k8s.gcr.io gcr.io quay.io your.own.registry another.public.registry" \
       -e AUTH_REGISTRIES="auth.docker.io:dockerhub_username:dockerhub_password your.own.registry:username:password" \
       rpardini/docker-registry-proxy:0.2.4

Let's say you did this on host 192.168.66.72, you can then curl http://192.168.66.72:3128/ca.crt and get the proxy CA certificate.

Configuring the Docker clients / Kubernetes nodes

On each Docker host that is to use the cache:

• Configure Docker proxy⁠ pointing to the caching server
• Add the caching server CA certificate to the list of system trusted roots.
• Restart dockerd

Do it all at once, tested on Ubuntu Xenial, which is systemd based:

# Add environment vars pointing Docker to use the proxy
mkdir -p /etc/systemd/system/docker.service.d
cat << EOD > /etc/systemd/system/docker.service.d/http-proxy.conf
[Service]
Environment="HTTP_PROXY=http://192.168.66.72:3128/"
Environment="HTTPS_PROXY=http://192.168.66.72:3128/"
EOD

# Get the CA certificate from the proxy and make it a trusted root.
curl http://192.168.66.72:3128/ca.crt > /usr/share/ca-certificates/docker_registry_proxy.crt
echo "docker_registry_proxy.crt" >> /etc/ca-certificates.conf
update-ca-certificates --fresh

# Reload systemd
systemctl daemon-reload

# Restart dockerd
systemctl restart docker.service

Testing

Clear dockerd of everything not currently running: docker system prune -a -fbeware

Then do, for example, docker pull k8s.gcr.io/kube-proxy-amd64:v1.10.4 and watch the logs on the caching proxy, it should list a lot of MISSes.

Then, clean again, and pull again. You should see HITs! Success.

Do the same for docker pull ubuntu and rejoice.

Test your own registry caching and authentication the same way; you don't need docker login, or .docker/config.json anymore.

Gotchas

• If you authenticate to a private registry and pull through the proxy, those images will be served to any client that can reach the proxy, even without authentication. beware
• Repeat, this will make your private images very public if you're not careful.
• Currently you cannot push images while using the proxy which is a shame. PRs welcome.
• Setting this on Linux is relatively easy. On Mac and Windows the CA-certificate part will be very different but should work in principle.

Why not use Docker's own registry, which has a mirror feature?

Yes, Docker offers Registry as a pull through cache⁠, unfortunately it only covers the DockerHub case. It won't cache images from quay.io, k8s.gcr.io, gcr.io, or any such, including any private registries.

That means that your shiny new Kubernetes cluster is now a bandwidth hog, since every image will be pulled from the Internet on every Node it runs on, with no reuse.

This is due to the way the Docker "client" implements --registry-mirror, it only ever contacts mirrors for images with no repository reference (eg, from DockerHub). When a repository is specified dockerd goes directly there, via HTTPS (and also via HTTP if included in a --insecure-registry list), thus completely ignoring the configured mirror.

Docker itself should provide this.

Yeah. Docker Inc should do it. So should NPM, Inc. Wonder why they don't. 😼

TODO:

• Allow using multiple credentials for DockerHub; this is possible since the /token request includes the wanted repo as a query string parameter.
• Test and make auth work with quay.io, unfortunately I don't have access to it (hint, hint, quay)
• Make the cache size configurable, today it's fixed at 32gb.
• Hide the mitmproxy building code under a Docker build ARG.
• I hope that in the future this can also be used as a "Developer Office" proxy, where many developers on a fast local network share a proxy for bandwidth and speed savings; work is ongoing in this direction.