Scratch Based .NET Core Images

Why?

Scratch based images start with no filesystem.

In this case we are extracting just the .NET Core framework and it's dependencies.

There are no other tools in the image, no distribution etc.

This makes the image smaller, gives you less reason to change the image because of the application dependencies and arguably makes the image more secure.

You'll have a more intimate understanding of what is running in your container because you put it there.

Any Gotchas?

Probably lots.

For instance if you want to make any https calls you'll want some certificate authority certificates.

You'll have to think about it but that isn't always a bad thing.

How Do I Use It?

Just like you normally would.

Make sure the dotnet version you use to build the application matches the version in the Dockerfile.

Here we are using 1.0.5

mkdir console
dotnet new console
dotnet restore
dotnet publish -c Release -o app

Create the following Dockerfile

FROM travelrepublic/dotnet:1.0.5-runtime
ADD app /app
ENTRYPOINT ["/usr/share/dotnet/dotnet", "/app/console.dll"]

and then

docker image build -t travelrepublic/consoleapp .
docker container run --rm travelrepublic/consoleapp

How Do I Debug It?

That is a bit more difficult.

Obviously there are no tools in the container itself.

You'll want to bring up another container in the same namespace/s as the dotnet container.

See here for a better explanation.

If you need to debug an initialisation issue you might have to consider copying something like strace to the application container.

There are probably better ways to do it though.