.Net 5 project Docker COPY file is not found

Question

I have a .Net 5 project called SaveGame with a Dockerfile generated automatically by Visual Studio. Checked many official tutorials and whatnot - the Dockerfile always looks the same.

#See https://aka.ms/containerfastmode to understand how Visual Studio uses this Dockerfile to build your images for faster debugging.

FROM mcr.microsoft.com/dotnet/aspnet:5.0-buster-slim AS base
WORKDIR /app
EXPOSE 80
EXPOSE 443

FROM mcr.microsoft.com/dotnet/sdk:5.0-buster-slim AS build
WORKDIR /src
COPY ["SaveGame.API/SaveGame.API.csproj", "SaveGame.API/"]
RUN dotnet restore "SaveGame.API/SaveGame.API.csproj"
COPY . .
WORKDIR "/src/SaveGame.API"
RUN dotnet build "SaveGame.API.csproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "SaveGame.API.csproj" -c Release -o /app/publish

FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "SaveGame.API.dll"]

Here's the folder with the Dockerfile:

Here's the folder with the project file:

I try to build a Docker image with a command

docker build -t savegame .

Yet the COPY command fails giving me this

[+] Building 0.4s (9/17)
 => [internal] load .dockerignore                                                                                  0.0s
 => => transferring context: 35B                                                                                   0.0s
 => [internal] load build definition from Dockerfile                                                               0.0s
 => => transferring dockerfile: 32B                                                                                0.0s
 => [internal] load metadata for mcr.microsoft.com/dotnet/sdk:5.0-buster-slim                                      0.3s
 => [internal] load metadata for mcr.microsoft.com/dotnet/aspnet:5.0-buster-slim                                   0.3s
 => CANCELED [build 1/7] FROM mcr.microsoft.com/dotnet/sdk:5.0-buster-slim@sha256:1ab344109a790d555aa9d618edc012a  0.0s
 => => resolve mcr.microsoft.com/dotnet/sdk:5.0-buster-slim@sha256:1ab344109a790d555aa9d618edc012a2f88781f01238fd  0.0s
 => [internal] load build context                                                                                  0.0s
 => => transferring context: 2.78kB                                                                                0.0s
 => CANCELED [base 1/2] FROM mcr.microsoft.com/dotnet/aspnet:5.0-buster-slim@sha256:76b29928ab5b442469c89cc7eb5f6  0.0s
 => => resolve mcr.microsoft.com/dotnet/aspnet:5.0-buster-slim@sha256:76b29928ab5b442469c89cc7eb5f6ef12d9e6e4139a  0.0s
 => CACHED [build 2/7] WORKDIR /src                                                                                0.0s
 => ERROR [build 3/7] COPY [SaveGame.API/SaveGame.API.csproj, SaveGame.API/]                                       0.0s
------
 > [build 3/7] COPY [SaveGame.API/SaveGame.API.csproj, SaveGame.API/]:
------
failed to solve with frontend dockerfile.v0: failed to build LLB: failed to compute cache key: "/SaveGame.API/SaveGame.API.csproj" not found: not found

Why does it not find the file?

EDIT:

Running it on Github -> Azure WebApp (Linux) deploy job, I get kinda same thing

Status: Downloaded newer image for mcr.microsoft.com/dotnet/sdk:5.0-buster-slim
 ---> 8eab6017c69e
Step 6/17 : WORKDIR /app
 ---> Running in bbe55e12dd3a
COPY failed: file not found in build context or excluded by .dockerignore: stat src/SaveGame.API/SaveGame.API.csproj,: file does not exist
Removing intermediate container bbe55e12dd3a
 ---> 595dc1db2583
Step 7/17 : COPY src/SaveGame.API/SaveGame.API.csproj, SaveGame.API/
Error: Process completed with exit code 1.

user_358535 · Answer

WORKDIR does not do what you expect it to do. It sets the current directory in the docker container. Use

COPY ["src/SaveGame.API/SaveGame.API.csproj", "SaveGame.API/"]

and it will work fine. Also, you will need to cd into the SaveGame.API before running dotnet restore if you don't have .sln file in the current directory.

user_9076736 · Answer

Because you run docker build -t savegame .. I believe that your current directory was repos/SaveGame.API and when docker run to the command COPY ["SaveGame.API/SaveGame.API.csproj", "SaveGame.API/"] there is no SaveGame.API directory in the current context to make a copy. It's nested under the src directory.

Edit that line to COPY ["src/SaveGame.API/SaveGame.API.csproj", "SaveGame.API/"]

.Net 5 project Docker COPY file is not found

2 Answers