One of the latest beta features of the open source Docker v2 Registry is the ability to act as a registry proxy cache for images hosted at Docker Hub. Running a registry cache allows you to store images locally, reducing redundant image pulls across the Internet from Docker Hub. This capability is helpful for users with a large amount of Docker Engines in their environment. Instead of having each Engine pull from the Docker Hub all the time, by following this tutorial you can allow these Engines to pull from the local registry proxy cache to save time and bandwidth.
Here’s how you can get started:
Requirements
• Docker Engine 1.8.3
• Docker Registry v2
• Disk space to store Docker images
• TLS certificate and key
Persistent data
In this example, we will assume that you are storing all of our persistent data on your local filesystem in the directory /data. This will include TLS certificate and key, configuration file, and cached images. We will mount this into the registry container later using a volume.
Securing your registry proxy cache
A registry proxy cache needs a TLS certificate to secure connections between the engines and registry hosting the cache. In this example, we will place our certificate (domain.crt) and key (domain.key) on our host in the /data directory. For additional information on securing a registry using TLS, see the Docker Registry 2.0 documentation.
Create a v2 registry proxy cache configuration
Next you will need to create a configuration file for the registry to act as a registry proxy cache. You can retrieve the default registry configuration file from the registry:2 image by using cat and a file redirection to create the configuration file:
$ docker run -it --rm --entrypoint cat registry:2 /etc/docker/registry/config.yml > /data/config.yml
I highly suggest retrieving the default configuration from the Docker image instead of using my example configuration as updates to the default configuration may occur over time.
Example default config.yml:
version: 0.1 log: fields service: registry storage: cache: layerinfo: inmemory filesystem: rootdirectory: /var/lib/registry http: addr: :5000
Update the ‘http’ section to configure TLS:
http: addr: :5000 tls: certificate: /var/lib/registry/domain.crt key: /var/lib/registry/domain.key
Add a ‘proxy’ section to your configuration file to enable the cache
Click here for the documentation
proxy: remoteurl: https://registry-1.docker.io username: [username] password: [password]
The ‘username’ and ‘password’ settings are optional. Providing a Docker Hub username and password will allow the registry proxy cache to store any private images hosted on Docker Hub that are accessible from that account. Any images accessible by that user will be accessible through your image cache.
Be sure to fully understand the implications of providing Docker Hub credentials and ensure your mirror is secure and access is restricted! If you are unsure, do not include a username and password and your registry proxy cache will only cache public images.
Start your registry proxy cache container
$ docker run -d --restart=always -p 5000:5000 --name v2-mirror -v /data:/var/lib/registry registry:2 /var/lib/registry/config.yml
The above command utilizes a volume to mount /data from our host into the container allowing for persistent storage of cached images, TLS certificate and key, and customized registry configuration.
Verify your registry proxy cache is up and running
$ curl -I https://mycache.example.com:5000/v2/ HTTP/1.1 200 OK Content-Length: 2 Content-Type: application/json; charset=utf-8 Docker-Distribution-Api-Version: registry/2.0 Date: Thu, 17 Sep 2015 21:42:02 GMT
Configure your Docker Engines to use the registry proxy cache
Update your Docker daemon arguments to include the --registry-mirror option:
--registry-mirror=https://<my-docker-mirror-host>:<port-number>
For example, if your host is named mycache.example.com and is running on port 5000, you would add the following option to the daemon arguments:
--registry-mirror=https://mycache.example.com:5000
Refer to Configuring and running Docker on various distributions for more info on how to add daemon arguments.
Test your registry proxy cache
Pull an image from Docker Hub you currently do not have stored locally. For example, the busybox:latest image:
$ docker pull busybox:latest
Check the catalog to verify that the busybox image has been cached:
$ curl https://mycache.example.com:5000/v2/_catalog
{"repositories":["library/busybox"]}
You can also verify that the latest tag has been cached:
$ curl https://mycache.example.com:5000/v2/library/busybox/tags/list
{"name":"library/busybox","tags":["latest"]}
Images will now be saved to your registry proxy cache as you pull them. Subsequent image pulls of images that have identical image manifests will be faster and the cache will maintain itself, purging images as they are no longer utilized.
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