This project is intended to enable modifying HTTP requests to Unix domain sockets on the fly by modifying values in the requests. The main.go file contains code to overwrite Docker registry locations in Docker client HTTP API requests, however unix_domain_socket_proxy will execute any function which accepts a *http.Request and modifies its fields.
This project uses Go's module functionality.
To build, which will pull dependencies the first time:
$ go build
To run,
$ ./docker-caching
The file main.go contains the main code, which defines where to look for the existing docker.sock file and where to put the proxy dockerproxy.sock file. It also contains a default value for which registry address to inject into docker pull requests.
To test, pull and run the docker registry image on a machine in the background. Just using simple localhost here but it could be bound to a public interface or passed through by a reverse proxy like NGINX.
$ docker pull registry
$ docker run -p 5000:5000 --restart always --name registry registry:2
The alpine-based registry can interfaced to through its own REST API, to tell it to populate from a high-level registry, however here we will just use a direct push example to populate the registry with an image. We will use ubuntu:18.04 merely as an example, and because it won't overlap with alpine layers in use by the registry.
$ docker pull ubuntu:18.04
$ docker tag ubuntu:18.04 localhost:5000/ubuntu:18.04
$ docker push localhost:5000/ubuntu:18.04
If you still were attached to or monitoring the standard out of the registry daemon you should have just seen some traffic indicating that something was pushed. A copy of ubuntu:18.04 should now be in our local registry.
Next we delete the copy from our host daemon's storage.
$ docker rmi ubuntu:18.04 localhost:5000/ubuntu:18.04
Next run the proxy in one shell.
$ ./docker-caching
And in another shell, issue a command from the docker client to the proxy socket. Here we will request ubuntu:18.04 but the proxy will redirect this image reference which is from the DockerHub registry, and point it instead at our localhost:5000 registry.
$ docker -D --host unix:///tmp/dockerproxy.sock pull ubuntu:18.04
Using default tag: latest
latest: Pulling from ubuntu
Digest: sha256:be159ff0e12a38fd2208022484bee14412680727ec992680b66cdead1ba76d19
Status: Image is up to date for localhost:5000/ubuntu:18.04
$ docker images
localhost:5000/ubuntu 18.04 47b19964fb50 4 weeks ago 88.1MB
Next steps:
- issue a docker tag API request to set the
localhost:5000/ubunturepository value for this image back to justubuntuafter the pull response from the daemon completes. This enables a client expecting theubuntu:18.04image to exist with that exact name, so futuredocker runor other commands are seamless after this redirection took place.