## TL,DR

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

## What?

Essentially, it's a [man in the middle](https://en.wikipedia.org/wiki/Man-in-the-middle_attack): an intercepting proxy based on `nginx`, to which all docker traffic is directed using the `HTTPS_PROXY` mechanism and injected CA root certificates. 

The main feature is Docker layer/image caching, including layers served from S3, Google Storage, etc. 

As a bonus it allows for centralized management of Docker registry credentials, which can in itself be the main feature, eg in Kubernetes environments.
 
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.

## master is unstable/beta

- `master` (and `:latest` Docker tag) is unstable
- Test version is `0.4.0-pre1`, see [0.4.0-pre1 tag on Github](https://github.com/rpardini/docker-registry-proxy/tree/0.4.0-pre1) - this image is multi-arch amd64/arm64
- Stable/production version is `0.3.0`, see [0.3.0 tag on Github](https://github.com/rpardini/docker-registry-proxy/tree/0.3.0) (amd64 only)

## Usage

- Run the proxy on a host close (network-wise: high bandwidth, same-VPC, etc) to the Docker clients
- Expose port 3128 to the network
- Map volume `/docker_mirror_cache` for up to `CACHE_MAX_SIZE` (32gb by default) of cached images across all cached registries
- Map volume `/ca`, the proxy will store the CA certificate here across restarts. **Important** this is security sensitive.
- Env `CACHE_MAX_SIZE` (default `32g`): set the max size to be used for caching local Docker image layers. Use [Nginx sizes](http://nginx.org/en/docs/syntax.html).
- Env `REGISTRIES`: space separated list of registries to cache; no need to include DockerHub, its already done internally.
- Env `AUTH_REGISTRIES`: space separated list of `hostname:username:password` authentication info.
  - `hostname`s listed here should be listed in the REGISTRIES environment as well, so they can be intercepted.
- Env `AUTH_REGISTRIES_DELIMITER` to change the separator between authentication info. By default, a space: "` `". If you use keys that contain spaces (as with Google Cloud Registry), you should update this variable, e.g. setting it to `AUTH_REGISTRIES_DELIMITER=";;;"`. In that case, `AUTH_REGISTRIES` could contain something like `registry1.com:user1:pass1;;;registry2.com:user2:pass2`.
- Env `AUTH_REGISTRY_DELIMITER` to change the separator between authentication info *parts*. By default, a colon: "`:`". If you use keys that contain single colons, you should update this variable, e.g. setting it to `AUTH_REGISTRIES_DELIMITER=":::"`. In that case, `AUTH_REGISTRIES` could contain something like `registry1.com:::user1:::pass1 registry2.com:::user2:::pass2`.

### Simple (no auth, all cache)
```bash
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 \
       rpardini/docker-registry-proxy:0.4.0-pre1
```

### DockerHub auth

For Docker Hub authentication:
- `hostname` should be `auth.docker.io`
- `username` should NOT be an email, use the regular username

```bash
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:0.4.0-pre1
```

### Simple registries auth (HTTP Basic auth)

For regular registry auth (HTTP Basic), the `hostname` should be the registry itself... unless your registry uses a different auth server.

See the example above for DockerHub, adapt the `your.own.registry` parts (in both ENVs).

This should work for quay.io also, but I have no way to test.

### GitLab auth

GitLab may use a different/separate domain to handle the authentication procedure.

Just like DockerHub uses `auth.docker.io`, GitLab uses its primary (git) domain for the authentication.

If you run GitLab on `git.example.com` and its registry on `reg.example.com`, you need to include both in `REGISTRIES` and use the primary domain for `AUTH_REGISTRIES`.

For GitLab.com itself the authentication domain should be `gitlab.com`.

```bash
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="reg.example.com git.example.com" \
       -e AUTH_REGISTRIES="git.example.com:USER:PASSWORD" \
       rpardini/docker-registry-proxy:0.4.0-pre1
```

### Google Container Registry (GCR) auth

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](https://cloud.google.com/container-registry/docs/advanced-authentication#json_key_file). 

The service account key is in JSON format, it contains spaces ("` `") and colons ("`:`"). 

To be able to use GCR you should set `AUTH_REGISTRIES_DELIMITER` to something different than space (e.g. `AUTH_REGISTRIES_DELIMITER=";;;"`) and `AUTH_REGISTRY_DELIMITER` to something different than a single colon (e.g. `AUTH_REGISTRY_DELIMITER=":::"`).

Example with GCR using credentials from a service account from a key file `servicekey.json`:

```bash
docker run --rm --name docker_registry_proxy -it \
       -p 0.0.0.0:3128:3128 \
       -v $(pwd)/docker_mirror_cache:/docker_mirror_cache \
       -v $(pwd)/docker_mirror_certs:/ca \
       -e REGISTRIES="k8s.gcr.io gcr.io quay.io your.own.registry another.public.registry" \
       -e AUTH_REGISTRIES_DELIMITER=";;;" \
       -e AUTH_REGISTRY_DELIMITER=":::" \
       -e AUTH_REGISTRIES="gcr.io:::_json_key:::$(cat servicekey.json);;;auth.docker.io:::dockerhub_username:::dockerhub_password" \
       rpardini/docker-registry-proxy:0.4.0-pre1
```

## Configuring the Docker clients / Kubernetes nodes

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

On each Docker host that is to use the cache:

- [Configure Docker proxy](https://docs.docker.com/config/daemon/systemd/#httphttps-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, Bionic, and Focal, all systemd based:

```bash
# 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 -f` *beware*

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.

## Developing/Debugging

Since `0.4.0` there is a separate `-debug` version of the image, which includes `nginx-debug`, and has `mitmproxy` (actually `mitmweb`) inserted after the CONNECT proxy but before the caching logic.
This allows very in-depth debugging, but tends to be unstable with huge layers. Use sparingly, and definitely not in production.

```bash
docker run --rm --name docker_registry_proxy -it 
       -e DEBUG_NGINX=true -e DEBUG=true -p 0.0.0.0:8081:8081 \
       -p 0.0.0.0:3128:3128 \
       -v $(pwd)/docker_mirror_cache:/docker_mirror_cache \
       -v $(pwd)/docker_mirror_certs:/ca \
       rpardini/docker-registry-proxy:0.4.0-pre1-debug
```

- `DEBUG=true` enables the mitmweb proxy, accessible on port 8081
- `DEBUG_NGINX=true` enables nginx-debug and debug logging, which probably is too much.

## 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.
  - Please send PRs with instructions for Windows and Mac if you succeed!

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

Yes, Docker offers [Registry as a pull through cache](https://docs.docker.com/registry/recipes/mirror/), *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:

- [ ] Test and make auth work with quay.io, unfortunately I don't have access to it (_hint, hint, quay_)
- [x] Hide the mitmproxy building code under a Docker build ARG.
- [ ] "Developer Office" proxy scenario, where many developers on a fast LAN share a proxy for bandwidth and speed savings (already works for pulls, but messes up pushes, which developers tend to use a lot)