What is a Docker registry service connection?

Question

Following this documentation, Docker registry service connection is found in the following YAML. What is Docker registry service connection and where can it be found?

trigger:
- master

variables:
  # Container registry service connection established during pipeline creation
  dockerRegistryServiceConnection: <Docker registry service connection>
  imageRepository: <Name of your image repository>
  containerRegistry: <Name of the Azure container registry>
  dockerfilePath: '$(Build.SourcesDirectory)/Dockerfile'
  tag: '$(Build.BuildId)'

  # Agent VM image name
  vmImageName: 'ubuntu-latest'

- task: AzureWebAppContainer@1 # Add this at the end of your file
  inputs:
    azureSubscription: '<Azure service connection>'
    appName: '<Name of the container web app>'
    containers: $(containerRegistry)/$(imageRepository):$(tag)

Answer 1

A service connection is a connector to an external service (see here). A Docker registry service connection basically is a connector to a Docker registry. You can set it here:

Answer 2

mmking's answer covers the what part of the question, but not where can it be found.

After adding a "Docker Registry" service connection, select it from the list of service connections. The url will look something like:

https://your-org.visualstudio.com/YourProject/_settings/adminservices?resourceId=0b6c0705-9fbb-40ec-b629-95cd92856257

Take the resourceId from the query string, which is "0b6c0705-9fbb-40ec-b629-95cd92856257" in the above example, and use it as the dockerRegistryServiceConnection value.