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I'm struggling to set up a CI process for a web application in Azure. I'm used to deploying built code directly into Web Apps in Azure but decided to use docker this time.

In the build pipeline, I build the docker images and push them to an Azure Container Registry, tagged with the latest build number. In the release pipeline (which has DEV, TEST and PROD), I need to deploy those images to the Web Apps of each environment. There are 2 relevant tasks available in Azure releases: "Azure App Service deploy" and "Azure Web App for Containers". Neither of these allow the image source for the Web App to be set to Azure Conntainer Registry. Instead they take custom registry/repository names and set the image source in the Web App to Private Registry, which then requires login and password. I'm also deploying all Azure resources using ARM templates so I don't like the idea of configuring credentials when the 2 resources (the Registry and the Web App) are integrated already. Ideally, I would be able to set the Web App to use the repository and tag in Azure Container Registry that I specify in the release. I even tried to manually configure the Web Apps first with specific repositories and tags, and then tried to change the tags used by the Web Apps with the release (with the tasks I mentioned) but it didn't work. The tags stay the same.

Another option I considered was to configure all Web Apps to specific and permanent repositories and tags (e.g. "dev-latest") from the start (which doesn't fit well with ARM deployments since the containers need to exist in the Registry before the Web Apps can be configured so my infrastructure automation is incomplete), enable "Continuous Deployment" in the Web Apps and then tag the latest pushed repositories accordingly in the release so they would be picked up by Web Apps. I could not find a reasoble way to add tags to existing repositories in the Registry.

What is Azure best practice for CI with containerised web apps? How do people actually build their containers and then deploy them to each environment?