AWS Lambda: .NET 9 container base image deprecation

The AWS Lambda supported runtimes table lists .NET 9 as ".NET 9 (container only)", and the AWS base images for .NET table lists a .NET 9 base image. Lambda's responsibility for updating the container base image ends at deprecation. Deprecation notifications are not available for functions that use container images. The customer is responsible for upgrading functions to use a supported runtime or base image.

1. Upgrade the function to a supported base image. AWS says to upgrade before the previous image is deprecated. The AWS base images for .NET table also lists a .NET 10 base image.
2. If you use your own Dockerfile, set the FROM property to the URI of the new base image. Use the same .NET version in the TargetFramework of the project file.
3. Create a new container image for the function: build the Docker image, upload it to Amazon ECR, and deploy it to the Lambda function. For a function defined as a container image, changing the runtime means creating a new container image.