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. What if the content changes on the Hub? Docker takes away repetitive, mundane configuration tasks and is used throughout the development lifecycle for fast, easy and portable application development - desktop and cloud. Docker’s comprehensive end to end platform includes UIs, CLIs, APIs and security that are engineered to work together across the entire application delivery lifecycle. Alternatively, you can set up a Docker Hub pull through registry mirror pre-configured with Docker Hub account credentials. Using a pull through registry mirror is potentially simpler than making many build config modifications. It may also bring additional performance improvements since network roundtrips to Docker Hub are reduced.

Docker Registry Mirrors For Sale

Use-case

If you have multiple instances of Docker running in your environment, such asmultiple physical or virtual machines all running Docker, each daemon goes outto the internet and fetches an image it doesn’t have locally, from the Dockerrepository. You can run a local registry mirror and point all your daemonsthere, to avoid this extra internet traffic.

Alternatives

Alternatively, if the set of images you are using is well delimited, you cansimply pull them manually and push them to a simple, local, private registry.

Furthermore, if your images are all built in-house, not using the Hub at all andrelying entirely on your local registry is the simplest scenario.

Gotcha

It’s currently not possible to mirror another private registry. Only the centralHub can be mirrored.

Solution

The Registry can be configured as a pull through cache. In this mode a Registryresponds to all normal docker pull requests but stores all content locally.

How does it work?

Docker Registry Mirror Quay.io

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

What if the content changes on the Hub?

When a pull is attempted with a tag, the Registry checks the remote toensure if it has the latest version of the requested content. Otherwise, itfetches and caches the latest content.

What about my disk?

In environments with high churn rates, stale data can build up in the cache.When running as a pull through cache the Registry periodically removes oldcontent to save disk space. Subsequent requests for removed content causes aremote fetch and local re-caching.

To ensure best performance and guarantee correctness the Registry cache shouldbe configured to use the filesystem driver for storage.

Run a Registry as a pull-through cache

The easiest way to run a registry as a pull through cache is to run the officialRegistry image.At least, you need to specify proxy.remoteurl within /etc/docker/registry/config.ymlas described in the following subsection.

Multiple registry caches can be deployed over the same back-end. A singleregistry cache ensures that concurrent requests do not pull duplicate data,but this property does not hold true for a registry cache cluster.

Docker Hub

Configure the cache

To configure a Registry to run as a pull through cache, the addition of aproxy section is required to the config file.

To access private images on the Docker Hub, a username and password canbe supplied.

Warning: If you specify a username and password, it’s very important tounderstand that private resources that this user has access to Docker Hub ismade available on your mirror. You must secure your mirror byimplementing authentication if you expect these resources to stay private!

Warning: For the scheduler to clean up old entries, delete mustbe enabled in the registry configuration. SeeRegistry Configuration for more details.

Configure the Docker daemon

Either pass the --registry-mirror option when starting dockerd manually,or edit /etc/docker/daemon.jsonand add the registry-mirrors key and value, to make the change persistent.

Save the file and reload Docker for the change to take effect.

Some log messages that appear to be errors are actually informational messages.

Check the level field to determine whetherthe message is warning you about an error or is giving you information.For example, this log message is informational:

It’s telling you that the file doesn’t exist yet in the local cache and isbeing pulled from upstream.

Use case: the China registry mirror

The URL of the registry mirror for China is registry.docker-cn.com. You canpull images from this mirror just like you do for other registries byspecifying the full path, including the registry, in your docker pullcommand, for example:

Docker Registry-mirrors Authentication

You can add 'https://registry.docker-cn.com' to the registry-mirrors arrayin /etc/docker/daemon.jsonto pull from the China registry mirror by default.

Save the file and reload Docker for the change to take effect.

Or, you can configure the Docker daemon with the --registry-mirror startupparameter: