moby--moby/docs/articles/registry_mirror.md

Run a local registry mirror

Why?

If you have multiple instances of Docker running in your environment (e.g., multiple physical or virtual machines, all running the Docker daemon), each time one of them requires an image that it doesn't have it will go out to the internet and fetch it from the public Docker registry. By running a local registry mirror, you can keep most of the image fetch traffic on your local network.

How does it work?

The first time you request an image from your local registry mirror, it pulls the image from the public Docker registry and stores it locally before handing it back to you. On subsequent requests, the local registry mirror is able to serve the image from its own storage.

How do I set up a local registry mirror?

There are two steps to set up and use a local registry mirror.

Step 1: Configure your Docker daemons to use the local registry mirror

You will need to pass the --registry-mirror option to your Docker daemon on startup:

docker --registry-mirror=http://<my-docker-mirror-host> -d

For example, if your mirror is serving on http://10.0.0.2:5000, you would run:

docker --registry-mirror=http://10.0.0.2:5000 -d

NOTE: Depending on your local host setup, you may be able to add the --registry-mirror options to the DOCKER_OPTS variable in /etc/default/docker.

Step 2: Run the local registry mirror

You will need to start a local registry mirror service. The registry image provides this functionality. For example, to run a local registry mirror that serves on port 5000 and mirrors the content at registry-1.docker.io:

docker run -p 5000:5000 \
    -e STANDALONE=false \
    -e MIRROR_SOURCE=https://registry-1.docker.io \
    -e MIRROR_SOURCE_INDEX=https://index.docker.io \
    registry

Test it out

With your mirror running, pull an image that you haven't pulled before (using time to time it):

$ time docker pull node:latest
Pulling repository node
[...]

real   1m14.078s
user   0m0.176s
sys    0m0.120s

Now, remove the image from your local machine:

$ docker rmi node:latest

Finally, re-pull the image:

$ time docker pull node:latest
Pulling repository node
[...]

real   0m51.376s
user   0m0.120s
sys    0m0.116s

The second time around, the local registry mirror served the image from storage, avoiding a trip out to the internet to refetch it.