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moby--moby/docs/sources/articles/registry_mirror.md
Tim Smith 69a75c673c Add daemon flag to specify public registry mirrors
Adds support for a --registry-mirror=scheme://<host>[:port]
daemon flag. The flag may be present multiple times. If
provided, mirrors are prepended to the list of endpoints used
for image pull. Note that only mirrors of the public
index.docker.io registry are supported, and image/tag resolution
is still performed via the official index.

Docker-DCO-1.1-Signed-off-by: Tim Smith <timbot@google.com> (github: timbot)
2014-09-09 19:03:38 +00:00

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page_title: Run a local registry mirror
page_description: How to set up and run a local registry mirror
page_keywords: docker, registry, mirror, examples
# 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/defaults/docker`.
### Step 2: Run the local registry mirror
You will need to start a local registry mirror service. The
[`registry` image](https://registry.hub.docker.com/_/registry/) 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.