How to set variable with default value at the pipeline level?

GitLab CI/CD
3

I found a way to create a kind of default variable scenario using rules using different variable names… but I think it would probably work using the same variable name too. This is how I did it:

dotnet_build:
  variables:
    DEFAULT_IMAGE: mcr.microsoft.com/dotnet/core/sdk:latest
  image: $IMAGE_NAME
  script:
    - dotnet build
  rules:
    - if: $IMAGE_OVERRIDE != null
      variables:
        IMAGE_NAME: $IMAGE_OVERRIDE
    - when: always
      variables:
        IMAGE_NAME: $DEFAULT_IMAGE

See discussion on the forum: Override / set default variable value