Allow trusted services to securely access a network-restricted container registry

With Azure Container Registry, you can allow select trusted Azure services to access a registry that's configured with network access rules. When you allow trusted services, a trusted service instance can securely bypass the registry's network rules and perform operations such as pulling or pushing images. This article explains how to enable and use trusted services with a network-restricted Azure container registry.

Use the Azure Cloud Shell or a local installation of the Azure CLI to run the command examples in this article. Use version 2.18 or later to run it locally. Run az --version to find the version. If you need to install or upgrade, see Install Azure CLI.

Limitations

• Certain registry access scenarios with trusted services require a managed identity for Azure resources. Except where noted that a user-assigned managed identity is supported, only a system-assigned identity can be used.
• Allowing trusted services doesn't apply to a container registry configured with a service endpoint. The feature only affects registries that are restricted with a private endpoint or that have public IP access rules applied.

About trusted services

Azure Container Registry has a layered security model that supports multiple network configurations to restrict access to a registry. These configurations include:

• Private endpoint with Azure Private Link. When configured, a registry's private endpoint is accessible only to resources within the virtual network, using private IP addresses.
• Registry firewall rules, which allow access to the registry's public endpoint only from specific public IP addresses or address ranges. You can also configure the firewall to block all access to the public endpoint when using private endpoints.

When you deploy a registry in a virtual network or configure it with firewall rules, it denies access to users or services from outside those sources.

Several multitenant Azure services operate from networks that you can't include in these registry network settings. As a result, these services can't perform operations such as pulling or pushing images to the registry. By designating certain service instances as "trusted", a registry owner can allow select Azure resources to securely bypass the registry's network settings to perform registry operations.

Trusted services

Instances of the following services can access a network-restricted container registry if the registry's allow trusted services setting is enabled (the default). More services will be added over time.

Where indicated, access by the trusted service requires additional configuration of a managed identity in a service instance, assignment of an RBAC role, and authentication with the registry. For example steps, see Trusted services workflow, later in this article.

Trusted service	Supported usage scenarios	Configure managed identity with RBAC role
Azure Container Instances	Deploy to Azure Container Instances from Azure Container Registry using a managed identity	Yes, either system-assigned or user-assigned identity
Microsoft Defender for Cloud	Vulnerability scanning by Microsoft Defender for container registries	No
ACR Tasks	Access the parent registry or a different registry from an ACR Task	Yes
Machine Learning	Deploy or train a model in a Machine Learning workspace using a custom Docker container image	Yes
Azure Container Registry	Import images to or from a network-restricted Azure container registry	No

Note

Currently, enabling the allow trusted services setting doesn't apply to App Service.

Allow trusted services - CLI

By default, the allow trusted services setting is enabled in a new Azure container registry. Disable or enable the setting by running the az acr update command.

To disable:

az acr update --name myregistry --allow-trusted-services false

To enable the setting in an existing registry or a registry where it's already disabled:

az acr update --name myregistry --allow-trusted-services true

Allow trusted services - portal

By default, the allow trusted services setting is enabled in a new Azure container registry.

To disable or re-enable the setting in the portal:

1. In the portal, navigate to your container registry.
2. Under Settings, select Networking.
3. In Allow public network access, select Selected networks or Disabled.
4. Do one of the following steps:
   • To disable access by trusted services, under Firewall exception, uncheck Allow trusted Microsoft services to access this container registry.
   • To allow trusted services, under Firewall exception, check Allow trusted Microsoft services to access this container registry.
5. Select Save.

Trusted services workflow

Here's a typical workflow to enable an instance of a trusted service to access a network-restricted container registry. This workflow is needed when you use a service instance's managed identity to bypass the registry's network rules.

1. Enable a managed identity in an instance of one of the trusted services for Azure Container Registry.
2. Assign the identity an Azure role to your registry. For example, assign the ACRPull role to pull container images.
3. Configure the setting in the network-restricted registry to allow access by trusted services.
4. Use the identity's credentials to authenticate with the network-restricted registry.
5. Pull images from the registry, or perform other operations allowed by the role.

Example: ACR Tasks

The following example demonstrates using ACR Tasks as a trusted service. For task details, see Cross-registry authentication in an ACR task using an Azure-managed identity.

1. Create or update an Azure container registry. Create an ACR task.
   • Enable a system-assigned managed identity when creating the task.
   • Disable default auth mode (--auth-mode None) of the task.
2. Assign the task identity an Azure role to access the registry. For example, assign the AcrPush role, which has permissions to pull and push images.
3. Add managed identity credentials for the registry to the task.
4. To confirm that the task bypasses network restrictions, disable public access in the registry.
5. Run the task. If the registry and task are configured properly, the task runs successfully, because the registry allows access.

To test disabling access by trusted services:

1. Disable the setting to allow access by trusted services.
2. Run the task again. In this case, the task run fails, because the registry no longer allows access by the task.

Next steps

• To restrict access to a registry using a private endpoint in a virtual network, see Configure Azure Private Link for an Azure container registry.
• To set up registry firewall rules, see Configure public IP network rules.