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.
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.
There are two steps to set up and use a local registry mirror.
You will need to pass the --registry-mirror
option to your Docker daemon on startup:
docker daemon --registry-mirror=http://<my-docker-mirror-host>
For example, if your mirror is serving on http://10.0.0.2:5000
, you would run:
docker daemon --registry-mirror=http://10.0.0.2:5000
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
.
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
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.