Docker Socket Proxy

What?

This is a security-enhanced proxy for the Docker Socket.

Why?

Giving access to your Docker socket could mean giving root access to your host, or even to your whole swarm, but some services require hooking into that socket to react to events, etc. Using this proxy lets you block anything you consider those services should not do.

How?

We use the official Alpine-based HAProxy image with a small configuration file.

It blocks access to the Docker socket API according to the environment variables you set. It returns a HTTP 403 Forbidden status for those dangerous requests that should never happen.

Security recommendations

Never expose this container's port to a public network. Only to a Docker networks where only reside the proxy itself and the service that uses it.
Revoke access to any API section that you consider your service should not need.
This image does not include TLS support, just plain HTTP proxy to the host Docker Unix socket (which is not TLS protected even if you configured your host for TLS protection). This is by design because you are supposed to restrict access to it through Docker's built-in firewall.
Read the docs for the API version you are using, and know what you are doing.

Usage

Run the API proxy (--privileged flag is required here because it connects with the docker socket, which is a privileged connection in some SELinux/AppArmor contexts and would get locked otherwise):
```
$ docker container run \
    -d --privileged \
    --name dockerproxy \
    -v /var/run/docker.sock:/var/run/docker.sock \
    -p 127.0.0.1:2375:2375 \
    tecnativa/docker-socket-proxy
```
Connect your local docker client to that socket:
```
$ export DOCKER_HOST=tcp://localhost:2375
```

You can see the docker version:

$ docker version
Client:
 Version:      17.03.1-ce
 API version:  1.27
 Go version:   go1.7.5
 Git commit:   c6d412e
 Built:        Mon Mar 27 17:14:43 2017
 OS/Arch:      linux/amd64

Server:
 Version:      17.03.1-ce
 API version:  1.27 (minimum version 1.12)
 Go version:   go1.7.5
 Git commit:   c6d412e
 Built:        Mon Mar 27 17:14:43 2017
 OS/Arch:      linux/amd64
 Experimental: false

You cannot see running containers:

$ docker container ls
Error response from daemon: <html><body><h1>403 Forbidden</h1>
Request forbidden by administrative rules.
</body></html>

The same will happen to any containers that use this proxy's 2375 port to access the Docker socket API.

Grant or revoke access to certain API sections

You grant and revoke access to certain features of the Docker API through environment variables.

Normally the variables match the URL prefix (i.e. AUTH blocks access to /auth/* parts of the API, etc.).

Possible values for these variables:

0 to revoke access.
1 to grant access.

Access granted by default

These API sections are mostly harmless and almost required for any service that uses the API, so they are granted by default.

EVENTS
PING
VERSION

Access revoked by default

Security-critical

These API sections are considered security-critical, and thus access is revoked by default. Maximum caution when enabling these.

AUTH
SECRETS
POST: When disabled, only GET and HEAD operations are allowed, meaning any section of the API is read-only.

Not always needed

You will possibly need to grant access to some of these API sections, which are not so extremely critical but can expose some information that your service does not need.

BUILD
COMMIT
CONFIGS
CONTAINERS
ALLOW_START (containers/id/start)
ALLOW_STOP (containers/id/stop)
ALLOW_RESTARTS (containers/id/stop|restart|kill)
DISTRIBUTION
EXEC
GRPC
IMAGES
INFO
NETWORKS
NODES
PLUGINS
SERVICES
SESSION
SWARM
SYSTEM
TASKS
VOLUMES

Use a different Docker socket location

If your OS stores its Docker socket in a different location and you are unable to bind mount it in your container specification, you can specify this via the SOCKET_PATH environment variable.

For example, balenaOS exposes its socket at /var/run/balena-engine.sock. To accommodate this, merely set the SOCKET_PATH environment variable to /var/run/balena-engine.sock.

Development

All the dependencies you need to develop this project (apart from Docker itself) are managed with poetry.

To set up your development environment, run:

poetry install

Testing

To run the tests locally, add --prebuild to autobuild the image before testing:

poetry run pytest --prebuild

By default, the image that the tests use (and optionally prebuild) is named docker-socket-proxy:local. If you prefer, you can build it separately before testing, and remove the --prebuild flag, to run the tests with that image you built:

docker image build -t docker-socket-proxy:local .
poetry run pytest

If you want to use a different image, export the DOCKER_IMAGE_NAME env variable with the name you want:

# To build it automatically
env DOCKER_IMAGE_NAME=my_custom_image poetry run pytest --prebuild

# To prebuild it separately
docker image build -t my_custom_image .
env DOCKER_IMAGE_NAME=my_custom_image poetry run pytest

Logging

You can set the logging level or severity level of the messages to be logged with the environment variable LOG_LEVEL. Default value is info. Possible values are: debug, info, notice, warning, err, crit, alert and emerg.

Supported API versions

Image tags

Right now, the only supported tags in our container images are the ones following this rules:

Each individual git released version will result in an image being tagged with the correspondent :{{version}}
:latest will refer to the latest released version in git.
:edge will be the version that is in the repo's master branch

Any other tag you find in our Docker Hub image is deprecated.

We recommend using [GitHub Container Registry][ghcr-img] instead.

Feedback

Please send any issues to the issue tracker. For other kind of feedback, you can use our forum.

[ghcr-img]: https://github.com/orgs/Tecnativa/packages/container/package/docker-socket-proxy

Tecnativa / docker-socket-proxy

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