I wrote an ASP.NET Core application which should run in a container using docker. This works, but the hole build process is relatively slow. The main bottleneck seems to be nuget. A lot of packages are referenced, and it take time to load all of them from the internet. This is done on every build since docker alwas start a new container.
My idea is to create a persistent dictionary on the host, where the packages are stored. So they don't have to be fetched on every build. dotnet restore has a parameter --packages where I can define a cache directory. But for this its required to pass a shared dictionary to the docker build command.
I found out that docker run has a -v parameter where i can pass /host/path:/container/path to share a folder from the host to the container. But this only works for docker run, not docker build. Also the COPY command doesn't fit here since it let me only copy files from the host to the container. First I had to copy the other way round (container to host).
So how can I create a cache directory which doesn't got disposed together with the container?
I found similar issues like this. Its composer there, but the problem of a persistent cache directory is the same. They use the -v parameter on docker run. But I can't understand how this solve the problem: In my understanding of docker, the dockerfile should build the application. This includes installing dependencies like NuGet-Packages for ASP.NET Core, bower and similar. So this should happen in the dockerfile, not when running the container.
