For more about Angry Caching Proxy, have a look at the upstream project at https://github.com/epeli/angry-caching-proxy
Huge props to Epeli for making a super useful bit of software :-)
This fork is mostly tweaking to the Angry Caching Proxy to allow it to be used like a really aggressive version of jpetazzo's squid-in-a-can Docker container.
By really aggressive, I mean it caches GET requests and HEAD requests to anywhere (except localhost...), and caches irrespective of the status code returned.
To use the container for caching Docker container traffic, it can be run as follows:
docker run --net host -d bgibson/angry-caching-proxy
iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to 8080
It only really supports http requests at this point (no https) - so the iptables rule forwards traffic on port 80 to the Angry Caching Proxy container.
It's also possible to add caching for http connections for the Docker daemon (eg ADDs in a Dockerfile) by setting the http_proxy environment variable before starting it (eg http_proxy=http://localhost:8080 docker -d), although this seems to break https connections (including docker pull-ing) because docker appears to use the http_proxy variable for https connections as well (and Angry Caching Proxy doesn't support ssl).
This is a very aggressive caching solution (caching HEADs doesn't seem super common, and caching irrespective of status code is against some kind of rfc)...
I was/am working on a project in Docker which does a whole heap of network requests for every dependency (looks to be about 10 per dependency, both HEADs and GETs...) and took a large number of minutes (seemed to be ~30 on first run, and up to something like 10 minutes otherwise). And it was annoying. With this caching present, the dependency resolution step (and "downloading") looks to take ~30 seconds... So for me it's a big win :-)