how to build dockerfile when there is a class library in another folder

Question

I have a dotnet project and a class library project like this:

..solution-folder/
                app1/
                   - app1.csproj
                   - dockerfile
                   - other files
                app2/
                   - app2.csproj
                   - dockerfile
                   - other files
                app3/
                   - app3.csproj
                   - dockerfile
                   - other files
                core/
                   - core.csproj
                   - other files

And this is dockerfiles for each app:

FROM mcr.microsoft.com/dotnet/sdk:6.0 AS core-build
WORKDIR /src/app/core
COPY ["../core/core.csproj", "/"]

it gives error for copy command. it says:

   3 |     WORKDIR /src/app/core
   4 |
   5 | >>> COPY ["../core/core.csproj", "/"]
    ------------------------------------
   ERROR: "/core/core.csproj": `not found`

I understand that going to parent foler by (..) is not supported for the build context. Looks like I have to move dockerfiles to the solution-folder. But There are multiple dockerfiles. Should I combine them? if yes, how to generate 3 images for 3 different apps?

Answer 1

The location you specify as the Docker "build context" is the root of all the stuff you have access to from within the build of the Dockerfile. All your COPY paths must be relative to that path and you can't go above it with ... So you need to set the build context directory so that you can access everything you need in the scope of that directory.