COPY . . command in Dockerfile for ASP.NET

Question

The Visual Studio tooling for Docker creates a Dockerfile for ASP.NET projects containing a COPY . . command as below:

WORKDIR /src
COPY *.sln .         


        

Answer 1

Some more pointers on the above from Scott Hanselman: https://www.hanselman.com/blog/OptimizingASPNETCoreDockerImageSizes.aspx

PRO TIP: Docker is smart about making intermediate images and doing the least work, but it's useful if we (the authors) do the right thing as well to help it out.

For example, see where we COPY the .csproj over and then do a "dotnet restore"? Often you'll see folks do a "COPY . ." and then do a restore. That doesn't allow Docker to detect what's changed and you'll end up paying for the restore on EVERY BUILD.

By making this two steps - copy the project, restore, copy the code, this means your "dotnet restore" intermediate step will be cached by Docker and things will be WAY faster.