docker-compose container not firing up - docker

Question

New to docker and I have an empty .NET Core API project and an empty vuejs frontend project. I simply want both to be up and running before beginning development. I have a project that has two docker files (one for the backend and one for the frontend). I have a docker-compose.yml file in which I am running the docker-compose up command and my frontend launches fine while my backend does not. I am running in Linux containers.
My project structure is the following
docker-compose.yml
version: '3.4'
services:
backend:
image: backend
build:
context: ./backend
dockerfile: Dockerfile
frontend:
image: frontend
build:
context: ./frontend
dockerfile: Dockerfile
Backend Dockerfile
FROM mcr.microsoft.com/dotnet/aspnet:5.0-focal AS base
WORKDIR /app
# Creates a non-root user with an explicit UID and adds permission to access the /app folder
# For more info, please refer to https://aka.ms/vscode-docker-dotnet-configure-containers
RUN adduser -u 5678 --disabled-password --gecos "" appuser && chown -R appuser /app
USER appuser
FROM mcr.microsoft.com/dotnet/sdk:5.0-focal AS build
WORKDIR /src
COPY ["backend/backend.csproj", "backend/"]
RUN dotnet restore "backend/backend.csproj"
COPY . .
WORKDIR "/src/backend"
RUN dotnet build "backend.csproj" -c Release -o /app/build
FROM build AS publish
RUN dotnet publish "backend.csproj" -c Release -o /app/publish
FROM base AS final
WORKDIR /app
COPY --from=publish /app/publish .
ENTRYPOINT ["dotnet", "backend.dll"]
Frontend Dockerfile
FROM node:lts-alpine
# install simple http server for serving static content
RUN npm install -g http-server
# make the 'app' folder the current working directory
WORKDIR /app
# copy both 'package.json' and 'package-lock.json' (if available)
COPY package*.json ./
# copy project files and folders to the current working directory (i.e. 'app' folder)
COPY . .
# install project dependencies
RUN npm install
# build app for production with minification
RUN npm run build
CMD [ "http-server", "dist" ]
Error when running docker-compose up
=> ERROR [backend build 7/7] RUN dotnet build "backend.csproj" -c Release -o /app/build 8.1s
=> [frontend 1/7] FROM docker.io/library/node:lts-alpine#sha256:dc92f36e7cd917816fa2df041d4e9081453366381a00f40398d99e9392e78664 0.0s
=> CANCELED [frontend internal] load build context 7.0s
=> => transferring context: 35.13MB 7.0s
------
> [backend build 7/7] RUN dotnet build "backend.csproj" -c Release -o /app/build:
#19 1.015 Microsoft (R) Build Engine version 16.11.1+3e40a09f8 for .NET
#19 1.015 Copyright (C) Microsoft Corporation. All rights reserved.
#19 1.015
#19 2.634 Determining projects to restore...
#19 3.501 All projects are up-to-date for restore.
#19 7.322 CSC : error CS5001: Program does not contain a static 'Main' method suitable for an entry point [/src/backend/backend.csproj]
#19 7.334
#19 7.334 Build FAILED.
#19 7.334
#19 7.334 CSC : error CS5001: Program does not contain a static 'Main' method suitable for an entry point [/src/backend/backend.csproj]
#19 7.334 0 Warning(s)
#19 7.334 1 Error(s)
#19 7.334

Answer 1

I'd guess you should look at the copy statements in your backend Dockerfile before the build step. Looks like youre copying your source files or your csproj file into the wrong directories.
Lets break down whats happening in the build stage of your backend Dockerfile:
FROM mcr.microsoft.com/dotnet/sdk:5.0-focal AS build # Use the public dotnet/sdk image as our base build image
WORKDIR /src # Set the current working directory inside our build image to /src
COPY ["backend/backend.csproj", "backend/"] # Copy the file ./backend/backend.csproj from our host file system into the build image to the directory ./backend (i.e. /src/backend)
RUN dotnet restore "backend/backend.csproj" # Restore our dotnet dependencies
COPY . . # Copy all files from the current directory on our host system to the current directory inside our build image (i.e. /src)
WORKDIR "/src/backend" # Set our current directory inside the build image to /src/backend
RUN dotnet build "backend.csproj" -c Release -o /app/build # Build our dotnet application
You are copying the entire directory into your build image and the resulting file structure would look something like this:
/src/
|- frontend/
| |- ...
|- backend/
|- Program.cs
|- Startup.cs
|- WeatherForcast.cs
|- backend.csproj
|...
|- backend/
|- backend.csproj
You're then executing a dotnet build against the file /src/backend/ which based on the folder structure you shared above expects your source files to be in the same folder.
In your backend Dockerfile try:
...
COPY ["backend/", "./backend/"]
RUN dotnet restore "backend/backend.csproj"
WORKDIR "/src/backend"
RUN dotnet build "backend.csproj" -c Release -o /app/build
...