Frequently asked questions - Azure Container Registry

Yes. Here is a template that you can use to create a registry.

Yes. See the documentation from Microsoft Defender for Cloud, Twistlock and Aqua.

See the documentation for Kubernetes and steps for Azure Kubernetes Service.

Before getting admin credentials, make sure the registry's admin user is enabled.

To get credentials using the Azure CLI:

az acr credential show -n myRegistry

Using Azure PowerShell:

Invoke-AzureRmResourceAction -Action listCredentials -ResourceType Microsoft.ContainerRegistry/registries -ResourceGroupName myResourceGroup -ResourceName myRegistry

Before getting admin credentials, make sure the registry's admin user is enabled.

To get the first password:

{
    "password": "[listCredentials(resourceId('Microsoft.ContainerRegistry/registries', 'myRegistry'), '2017-10-01').passwords[0].value]"
}

To get the second password:

{
    "password": "[listCredentials(resourceId('Microsoft.ContainerRegistry/registries', 'myRegistry'), '2017-10-01').passwords[1].value]"
}

The error is seen when the user has permissions on a registry but doesn't have Reader-level permissions on the subscription. To resolve this issue, assign Reader permissions on the subscription to the user:

az role assignment create --role "Reader" --assignee user@contoso.com --scope /subscriptions/<subscription_id> 

It takes some time to propagate firewall rule changes. After you change firewall settings, please wait for a few minutes before verifying this change.

ACR supports Docker Registry HTTP API V2. The APIs can be accessed at https://<your registry login server>/v2/. Example: https://mycontainerregistry.azurecr.io/v2/

If you are on bash:

az acr manifest list-metadata --name myRepository --registry myRegistry --query "[?tags[0]==null].digest" --output tsv  | xargs -I% az acr repository delete --name myRegistry ---image myRepository@%

For PowerShell:

az acr manifest list-metadata --name myRepository --repository myRegistry --query "[?tags[0]==null].digest" --output tsv | %{ az acr repository delete --name myRegistry --image myRepository@$_ }

For more information, see Delete container images in Azure Container Registry.

This situation can happen if the underlying layers are still being referenced by other container images. If you delete an image with no references, the registry usage updates in a few minutes.

Create an image with a 1GB layer using the following docker file. This ensures that the image has a layer that isn't shared by any other image in the registry.

FROM alpine
RUN dd if=/dev/urandom of=1GB.bin  bs=32M  count=32
RUN ls -lh 1GB.bin

Build and push the image to your registry using the docker CLI.

docker build -t myregistry.azurecr.io/1gb:latest .
docker push myregistry.azurecr.io/1gb:latest

You should be able to see that the storage usage has increased in the Azure portal, or you can query usage using the CLI.

az acr show-usage -n myregistry

Delete the image using the Azure CLI or portal and check the updated usage in a few minutes.

az acr repository delete -n myregistry --image 1gb

You need to run the Azure CLI container by mounting the Docker socket:

docker run -it -v /var/run/docker.sock:/var/run/docker.sock azuresdk/azure-cli-python:dev

In the container, install docker:

apk --update add docker

Then authenticate with your registry:

az acr login -n MyRegistry

Enable TLS 1.2 by using any recent docker client (version 18.03.0 and above).

Yes, you can use trusted images in Azure Container Registry, since the Docker Notary has been integrated and can be enabled. For details, see Content Trust in Azure Container Registry.

Where is the file for the thumbprint located?

Under ~/.docker/trust/tuf/myregistry.azurecr.io/myrepository/metadata:

• Public keys and certificates of all roles (except delegation roles) are stored in the root.json.
• Public keys and certificates of the delegation role are stored in the JSON file of its parent role (for example targets.json for the targets/releases role).

It's suggested to verify those public keys and certificates after the overall TUF verification done by the Docker and Notary client.

ACR supports custom roles that provide different levels of permissions. Specifically, AcrPull and AcrPush roles allow users to pull and/or push images without the permission to manage the registry resource in Azure.

• Azure portal: Your registry -> Access Control (IAM) -> Add (Select AcrPull or AcrPush for the Role).

• Azure CLI: Find the resource ID of the registry by running the following command:

  az acr show -n myRegistry
  

  Then you can assign the AcrPull or AcrPush role to a user (the following example uses AcrPull):

  az role assignment create --scope resource_id --role AcrPull --assignee user@example.com
  

  Or, assign the role to a service principal identified by its application ID:

  az role assignment create --scope resource_id --role AcrPull --assignee 00000000-0000-0000-0000-000000000000
  

The assignee is then able to authenticate and access images in the registry.

• To authenticate to a registry:

  az acr login -n myRegistry 
  

• To list repositories:

  az acr repository list -n myRegistry
  

• To pull an image:

  docker pull myregistry.azurecr.io/hello-world
  

With the use of only the AcrPull or AcrPush role, the assignee doesn't have the permission to manage the registry resource in Azure. For example, az acr list or az acr show -n myRegistry won't show the registry.

Image quarantine is currently a preview feature of ACR. You can enable the quarantine mode of a registry so that only those images which have successfully passed security scan are visible to normal users. For details, see the ACR GitHub repo.

For more information, see Make your registry content publicly available.

A non-distributable layer in a manifest contains a URL parameter that content may be fetched from. Some possible use cases for enabling non-distributable layer pushes are for network restricted registries, air-gapped registries with restricted access, or for registries with no internet connectivity.

For example, if you have NSG rules set up so that a VM can pull images only from your Azure container registry, Docker will pull failures for foreign/non-distributable layers. For example, a Windows Server Core image would contain foreign layer references to Azure container registry in its manifest and would fail to pull in this scenario.

To enable pushing of non-distributable layers:

1. Edit the daemon.json file, which is located in /etc/docker/ on Linux hosts and at C:\ProgramData\docker\config\daemon.json on Windows Server. Assuming the file was previously empty, add the following contents:

   {
     "allow-nondistributable-artifacts": ["myregistry.azurecr.io"]
   }
   

   Note

   The value is an array of registry addresses, separated by commas.

2. Save and exit the file.

3. Restart Docker.

When you push images to the registries in the list, their non-distributable layers are pushed to the registry.

To troubleshoot common environment and registry issues, see Check the health of an Azure container registry.

• If this error is a transient issue, then retry will succeed.
• If docker pull fails continuously, then there could be a problem with the Docker daemon. The problem can generally be mitigated by restarting the Docker daemon.
• If you continue to see this issue after restarting Docker daemon, then the problem could be some network connectivity issues with the machine. To check if general network on the machine is healthy, run the following command to test endpoint connectivity. The minimum az acr version that contains this connectivity check command is 2.2.9. Upgrade your Azure CLI if you are using an older version.

az acr check-health -n myRegistry

• You should always have a retry mechanism on all Docker client operations.

Use the speed tool to test your machine network download speed. If machine network is slow, consider using Azure VM in the same region as your registry to improve network speed.

Use the speed tool to test your machine network upload speed. If machine network is slow, consider using Azure VM in the same region as your registry to improve network speed.

This error can happen with the Red Hat version of the Docker daemon, where --signature-verification is enabled by default. You can check the Docker daemon options for Red Hat Enterprise Linux (RHEL) or Fedora by running the following command:

grep OPTIONS /etc/sysconfig/docker

For instance, Fedora 28 Server has the following docker daemon options:

OPTIONS='--selinux-enabled --log-driver=journald --live-restore'

With --signature-verification=false missing, docker pull fails with an error similar to:

Trying to pull repository myregistry.azurecr.io/myimage ...
unauthorized: authentication required

To resolve the error:

1. Add the option --signature-verification=false to the Docker daemon configuration file /etc/sysconfig/docker. For example:

   OPTIONS='--selinux-enabled --log-driver=journald --live-restore --signature-verification=false'

2. Restart the Docker daemon service by running the following command:

   sudo systemctl restart docker.service
   

Details of --signature-verification can be found by running man dockerd.

Make sure you use an all lowercase server URL, for example, docker push myregistry.azurecr.io/myimage:latest, even if the registry resource name is uppercase or mixed case, like myRegistry.

Start dockerd with the debug option. First, create the Docker daemon configuration file (/etc/docker/daemon.json) if it doesn't exist, and add the debug option:

{    
    "debug": true    
}

Then, restart the daemon. For example, with Ubuntu 14.04:

sudo service docker restart

Details can be found in the Docker documentation.

• The logs may be generated at different locations, depending on your system. For example, for Ubuntu 14.04, it's /var/log/upstart/docker.log.
  See Docker documentation for details.

• For Docker for Windows, the logs are generated under %LOCALAPPDATA%/docker/. However it may not contain all the debug information yet.

  In order to access the full daemon log, you may need some extra steps:

  docker run --privileged -it --rm -v /var/run/docker.sock:/var/run/docker.sock -v /usr/local/bin/docker:/usr/local/bin/docker alpine sh
  
  docker run --net=host --ipc=host --uts=host --pid=host -it --security-opt=seccomp=unconfined --privileged --rm -v /:/host alpine /bin/sh
  chroot /host
  

  Now you have access to all the files of the VM running dockerd. The log is at /var/log/docker.log.

When you grant new permissions (new roles) to a service principal, the change might not take effect immediately. There are two possible reasons:

• Microsoft Entra role assignment delay. Normally it's fast, but it could take minutes due to propagation delay.

• Permission delay on ACR token server could take up to 10 minutes. To mitigate, you can docker logout and then authenticate again with the same user after 1 minute:

  docker logout myregistry.azurecr.io
  docker login myregistry.azurecr.io
  

Currently ACR doesn't support home replication deletion by the users. The workaround is to include the home replication create in the template but skip its creation by adding "condition": false as shown below:

{
    "name": "[concat(parameters('acrName'), '/', parameters('location'))]",
    "condition": false,
    "type": "Microsoft.ContainerRegistry/registries/replications",
    "apiVersion": "2017-10-01",
    "location": "[parameters('location')]",
    "properties": {},
    "dependsOn": [
        "[concat('Microsoft.ContainerRegistry/registries/', parameters('acrName'))]"
     ]
},

You may encounter an InvalidAuthenticationInfo error, especially using the curl tool with the option -L, --location (to follow redirects). For example, fetching the blob using curl with -L option and basic authentication:

curl -L -H "Authorization: basic $credential" https://$registry.azurecr.io/v2/$repository/blobs/$digest

may result in the following response:

<?xml version="1.0" encoding="utf-8"?>
<Error><Code>InvalidAuthenticationInfo</Code><Message>Authentication information is not given in the correct format. Check the value of Authorization header.
RequestId:00000000-0000-0000-0000-000000000000
Time:2019-01-01T00:00:00.0000000Z</Message></Error>

The root cause is that some curl implementations follow redirects with headers from the original request.

To resolve the problem, you need to follow redirects manually without the headers. Print the response headers with the -D - option of curl and then extract: the Location header:

REDIRECT_URL=$(curl -s -D - -H "Authorization: basic $credential" https://$registry.azurecr.io/v2/$repository/blobs/$digest | grep "^Location: " | cut -d " " -f2 | tr -d '\r')
curl $REDIRECT_URL

If you're using the Microsoft Edge/IE browser, you can see at most 100 repositories or tags. If your registry has more than 100 repositories or tags, we recommend that you use either the Firefox or Chrome browser to list them all.

The browser might not be able to send the request for fetching repositories or tags to the server. There could be various reasons such as:

• Lack of network connectivity
• Firewall
• Using the portal from a public network for a registry that allows only private access
• Ad blockers
• DNS errors

Please contact your network administrator or check your network configuration and connectivity. Try running az acr check-health -n yourRegistry using your Azure CLI to check if your environment is able to connect to the Container Registry. In addition, you could also try an incognito or private session in your browser to avoid any stale browser cache or cookies.

Here are some scenarios where operations may be disallowed:

• Classic registries are no longer supported. Please upgrade to a supported service tier using az acr update or the Azure portal.
• The image or repository maybe locked so that it can't be deleted or updated. You can use the az acr repository show command to view current attributes.
• Some operations are disallowed if the image is in quarantine. Learn more about quarantine.
• Your registry may have reached its storage limit.

If you see an error such as "unsupported repository format", "invalid format", or "the requested data does not exist" when specifying a repository name in repository operations, check the spelling and case of the name. Valid repository names can only include lowercase alphanumeric characters, periods, dashes, underscores, and forward slashes.

Prerequisites

• Enable decrypting HTTPS in Fiddler
• Enable Docker to use a proxy via the Docker UI.
• Be sure to revert when complete. Docker won't work with this enabled and Fiddler not running.

Windows containers

Configure Docker proxy to 127.0.0.1:8888

Linux containers

Find the ip of the Docker vm virtual switch:

(Get-NetIPAddress -InterfaceAlias "*Docker*" -AddressFamily IPv4).IPAddress

Configure the Docker proxy to output of the previous command and the port 8888 (for example 10.0.75.1:8888)

The following commands cancel all running tasks in the specified registry.

az acr task list-runs -r $myregistry --run-status Running --query '[].runId' -o tsv \
| xargs -I% az acr task cancel-run -r $myregistry --run-id %

If you pass a local source folder to the az acr build command, the .git folder is excluded from the uploaded package by default. You can create a .dockerignore file with the following setting. It tells the command to restore all files under .git in the uploaded package.

!.git/**

This setting also applies to the az acr run command.

We currently don't support GitLab for Source triggers.

Run Error Message Troubleshooting

CI/CD integration

• CircleCI
• GitHub Actions

Set up the correct firewalls rules to the existing network security groups or user-defined routes. After the setup, wait a few minutes for the firewall rules to apply.

The following Azure built-policy, when set to respective policy status, will block the user from enabling admin user on their registry.

Next steps

• Learn more about Azure Container Registry.