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Transparent proxy for docker containers, run in a docker container
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test Updated documentation to explain how to use HTTPS proxying Apr 7, 2016
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mime.conf Made the CA cert available for download from the squid proxy Apr 6, 2016
squid3.patch Reusing CA certificate Apr 7, 2016


Transparent caching proxy server for Docker containers, run in a Docker container. It can speed up the dependency-fetching part of your application build process.

Instructions for Use

First check out the code. Then build with:

sudo docker build -t docker-proxy .

Then run with:


The script will start the container and set up the appropriate routing rules. Your other Docker containers will automatically use the proxy, whether or not they were already running. When you are finished, just press CtrlC to stop the proxy.

NOTE: This project is not designed to be run with a simple docker run - it requires to be run on the docker host, so it can adjust the routing rules. You will need to check this code out and run on the host. For OS X, that's on your boot2docker, Docker Machine or similar host). To start under Docker Machine on OS X:

docker-machine scp default:/home/docker/
docker-machine ssh default
sh ./

Overview will fire up a Docker container running Squid, with appropriate firewall rules in place for transparent proxying. It will also configure port-based routing on the main host such that any traffic from a Docker container to port 80 routes via the transparent proxy container. It requires sudo access to perform the firewall changes, and it will prompt you for your password as appropriate. is designed to run in the foreground, because when the container terminates it needs to remove the rules that were redirecting the traffic.

If you want to see Squid in operation, you can (in another terminal) attach to the docker-proxy container - it is tailing the access log, so will show a record of requests made.

HTTPS Support

The proxy server supports HTTPS caching via Squid's SSL Bump feature. To enable it, start with:

./ ssl

The server will decrypt traffic from the server and encrypt it again using its own root certificate. HTTPS connections from your other Docker containers will fail until you install the root certificate. To install it:

  1. Install the ca-certificates package (Debian/Ubuntu images)
  2. Run

Those steps can be performed in a running container (for testing), or you can add them to your Dockerfile. can be run after you install your OS packages with apt, because apt shouldn't need HTTPS. However, adding PPAs with add-apt-repository will fail until the certificate is installed. See test/Dockerfile for an example.

Some programs don't use the OS's primary key store, such as npm and pip. You may need to take extra steps for those programs.

To test HTTPS support, do this in another console after starting the proxy:

cd test
sudo docker build -t test-proxy .
sudo docker run --rm test-proxy
# Should print "All tests passed"


This proxy configuration is intended to be used solely to speed up development of Docker applications. Do not attempt to use this to eavesdrop on other people's connections.

There exists a real possibility this script will break your iptables or ip rules in some unexpected way. Be aware that if things go wrong, the potential exists for all containers to lose the ability to download anything.

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