Configure where images are stored

Estimated reading time: 7 minutes

After installing Docker Trusted Registry, one of your first tasks is to designate and configure the Trusted Registry storage backend. This document provides the following:

  • Information describing your storage backend options.
  • Configuration steps using either the Trusted Registry UI or a YAML file.

While there is a default storage backend, filesystem, the Trusted Registry offers other options that are cloud-based. This flexibility to configure to a different storage backend allows you to:

  • Scale your Trusted Registry
  • Leverage storage redundancy
  • Store your images anywhere in the cloud
  • Take advantage of other features that are critical to your organization

At first, you might have explored Docker Trusted Registry and Docker Engine by installing them on your system to familiarize yourself with them. However, for various reasons such as deployment purposes or continuous integration, it makes sense to think about your long term organization’s needs when selecting a storage backend. The Trusted Registry natively supports TLS and basic authentication. It also ships with a notification system, calling webhooks in response to activity. The notification system also provides both extensive logging and reporting, which is useful for organizations that want to collect metrics.

Understand the Trusted Registry storage backend

By default, your Trusted Registry data resides as a data volume on the host filesystem. This is where your repositories and images are stored. This storage driver is the local posix filesystem and is configured to use a directory tree in the local filesystem. It’s suitable for development or small deployments. The filesystem can be located on the same computer as the Trusted Registry, or on a separate system.

Additionally, the Trusted Registry supports these cloud-based storage drivers:

  • Amazon Simple Storage Solution S3
  • OpenStack Swift
  • Microsoft Azure Blob Storage

Filesystem

If you select filesystem, then the Trusted Registry uses the local disk to store registry files. This backend has a single, required rootdirectory parameter which specifies a subdirectory of /var/local/dtr/imagestorage in which all registry files are stored. The default value of /local means the files are stored in /var/local/dtr/image-storage/local.

The Trusted Registry stores all its data at this location, so ensure there is adequate space available. To do so, you can run the following commands:

  • To analyze the disk usage: docker exec -it <container_name> bash then run df -h.
  • To see the file size of your containers, use the -s argument of docker ps -s.

Amazon S3

S3 stores data as objects within “buckets” where you read, write, and delete objects in that container. It too, has a rootdirectory parameter. If you select this option, there will be some tasks that you need to first perform on AWS.

  1. You must create an S3 bucket, and write down its name and the AWS zone it runs on.
  2. Determine write permissions for your bucket.
  3. S3 flavor comes with DEBUG=false by default. If you need to debug, then you need to add -e DEBUG=True.
  4. Specify an AWS region, which is dependent on your S3 location, for example, use -e AWS_REGION=”eu-west-1”.
  5. Ensure your host time is correct. If your host clock is still running on the main computer, but not on the docker host virtual machine, then you will have time differences. This may cause an issue if you try to authenticate with Amazon web services.
  6. You will also need your AWS access key and secret key. Learn more about it here.

Conversely, you can further limit what users access in the Trusted Registry when you use AW to host your Trusted Registry. Instead of using the UI to enter information, you can create an IAM user policy which is a JSON description of the effects, actions, and resources available to a user. The advantage of using this method instead of configuring through the Trusted Registry UI is that you can restrict what users can access. You apply the policy as part of the process of installing the Trusted Registry on AW. To set a policy through the AWS command line, save the policy into a file, for example TrustedRegistryUserPerms.json, and pass it to the put-user-policy AWS command:

$ aws iam put-user-policy --user-name MyUser --policy-name TrustedRegistryUserPerms --policy-document file://C:\Temp\TrustedRegistryUserPerms.json

You can also set a policy through your AWS console. For more information about setting IAM policies using the command line or the console, review the AWS Overview of IAM Policies article or visit the console Policies page.

The following example describes the minimum permissions set which allows Trusted Registry users to access, push, pull, and delete images.

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Effect": "Allow",
            "Action": "s3:ListAllMyBuckets",
            "Resource": "arn:aws:s3:::*"
        },
        {
            "Effect": "Allow",
            "Action": [
                "s3:ListBucket",
                "s3:GetBucketLocation"
            ],
            "Resource": "arn:aws:s3:::<INSERT YOUR BUCKET HERE>"
        },
        {
            "Effect": "Allow",
            "Action": [
                "s3:PutObject",
                "s3:GetObject",
                "s3:DeleteObject"
            ],
            "Resource": "arn:aws:s3:::<INSERT YOUR BUCKET HERE>/*"
        }
    ]
}

OpenStack Swift

OpenStack Swift, also known as OpenStack Object Storage, is an open source object storage system that is licensed under the Apache 2.0 license. Refer to Swift documentation to get started.

Microsoft Azure

This storage backend uses Microsoft’s Azure Blob storage. Data is stored within a paid Windows Azure storage account. Refer to Microsoft’s Azure documentation which explains how to set up your Storage account.

Configure your Trusted Registry storage backend

Once you select your driver, you need to configure it through the UI or use a YAML file (which is discussed further in this document.)

  1. From the main Trusted Registry screen, navigate to Settings > Storage.
  2. Under Storage Backend, use the drop down menu to select your storage. The screen refreshes to reflect your option.
  3. Enter your configuration settings. If you’re not sure what a particular parameter does, then find your driver from the following headings so that you can see a detailed explanation.
  4. Click Save. The Trusted Registry restarts so that your changes take effect.

Note: Changing your storage backend requires you to restart the Trusted Registry.

See the Registry configuration documentation for the full options specific to each driver. Storage drivers can be customized through the Docker Registry storage driver API.

Filesystem settings

The filesystem storage backend has only one setting, the “Storage directory”.

S3 settings

If you select the S3 storage backend, then you need to set “AWS region”, “Bucket name”, “Access Key”, and “Secret Key”.

Azure settings

Set the “Account name”, “Account key”, “Container”, and “Realm” on the Azure storage backend page.

Openstack Swift settings

View the Openstack Swift settings documentation so that you can set up your storage settings: authurl, username, password, container, tenant, tenantid, domain, domainid, insecureskipverify, region, chunksize, and prefix.

Configure using a YAML file

If the previous quick setup options are not sufficient to configure your Registry options, you can upload a YAML file. The schema of this file is identical to that used by the Registry.

There are several benefits to using a YAML file as it can provide an additional level of granularity in defining your storage backend. Advantages include:

  • Overriding specific configuration options.
  • Overriding the entire configuration file.
  • Selecting from the entire list of configuration options.

To configure:

  1. Navigate to the Trusted Registry UI > Settings > Storage.

  2. Select Download to get the text based file. It contains a minimum amount of information and you’re going to need additional data based on your driver and business requirements.

  3. Go here to see the open source YAML file. Copy the sections you need and paste into your storage.yml file. Some settings may contradict others, so ensure your choices make sense.

  4. Save the YAML file and return to the UI.

  5. On the Storage screen, upload the file, review your changes, and click Save.

See also

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