How to authenticate with Azure ACR from Azure container app service

Question

I'm trying to set up my App Container Service so that it can pull docker images from our ACR using Managed Identity, rather than storing the username and password in the app settings (apart from anything else we want to script these deployments and if the username and password are needed by the app service then we'd have to store them in source control).

Unbelievably, I cannot find any docs on this scenario. The closest I've found is using Managed Identity to pull an ACR image from a VM [https://learn.microsoft.com/en-us/azure/container-registry/container-registry-authentication-managed-identity] , which I can't use as a guide as the final step (the only bit I'm missing) is to SSH into the VM and run az acr login --name myContainerRegistry at the command line.

Where I've got to:

• I've created the ACR and the Container App Service
• I've granted the role ACR Pull and Reader to the system-assigned Identity of the app service
• The app service is getting access denied when trying to pull the container image

I don't know what to do next; like I said, I can't find any guides on this scenario.

Examinant

I'm not sure if this is possible. But an alternative is to access the Azure Key Vault from your deployment pipeline to fetch the credentials and inject them into the az webapp config container set command. And note that that's only necessary when deploying a new environment, not for every code deployment. Deploying environments is infrastructure automation rather than CI/CD. learn.microsoft.com/en-us/azure/devops/pipelines/tasks/deploy/… – Regulator

Thanks, although I'm not sure if that's going to work for us since we're using Terraform rather than ARM or the CLI directly. – Examinant

Answer 1

To configure the App Service to pull from ACR, you can use the service principal approach and setup the access level as you already done.

https://github.com/Azure/app-service-linux-docs/blob/master/service_principal_auth_acr.md

as far as App Service with terraform goes, you could inject the settings for the ServicePrincipal credentials secret in Azure Key Vault using

https://www.terraform.io/docs/providers/azurerm/r/app_service.html#app_settings

Hazen

Thanks @djsly, I used your idea to put the password in a key vault instance so that now my terraform state contains only a key vault reference (learn.microsoft.com/en-gb/azure/app-service/…) as the app setting, not the password itself – Examinant

Just a note that terraform now supports the setting to use MSI credentials to connect to the ACR. This is normally the preferred approach if your app is running in Azure as it doesn't require exposing SP credentials: registry.terraform.io/providers/hashicorp/azurerm/latest/docs/… – Slatternly

Answer 2

This is now possible by setting the acrUseManagedIdentityCreds property

Here is a tutorial with the steps: https://learn.microsoft.com/en-us/azure/app-service/tutorial-custom-container?pivots=container-linux#configure-app-service-to-deploy-the-image-from-the-registry

Here are the specific commands

1. Grant the managed identity permission to access the container registry:

az role assignment create --assignee <principal-id> --scope /subscriptions/<subscription-id>/resourceGroups/myResourceGroup/providers/Microsoft.ContainerRegistry/registries/<registry-name> --role "AcrPull"

2. Configure your app to use the managed identity to pull from Azure Container Registry

az resource update --ids /subscriptions/<subscription-id>/resourceGroups/myResourceGroup/providers/Microsoft.Web/sites/<app-name>/config/web --set properties.acrUseManagedIdentityCreds=True

Jere

Answer 3

There is a mistake that you understand the Managed Identity of the Web App. The Managed Identity of the Web App is used to access other resources inside the web app container. It means the web app container is already running. But when you pull the image, the container does not run well. So it's impossible to use the Managed Identity to pull the images from ACR. You only can use the username and password to pull the images from ACR as it does.

Upheave

Answer 4

For people doing Azure ML and getting the following error:

AzureMLCompute job failed.
AggregatedUnauthorizedAccessError: Failed to pull Docker image aaa.azurecr.io/bbb:latest. 
This error may occur because the compute could not authenticate with the Docker registry to pull the image. 
If using ACR please ensure the ACR has Admin user enabled or a Managed Identity with `AcrPull` access to the ACR is assigned to the compute. 
If the ACR Admin user's password was changed recently it may be necessary to synchronize the workspace keys.
Authentication methods attempted: Anonymous

You need to create compute with managed identity to access Docker images for training [this and this].

Petulah