Working .NET multi-arch Docker build (ARM + Intel)

docker-build.sh

#!/bin/sh
docker buildx build --platform linux/amd64,linux/arm64 .

Dockerfile

# See https://devblogs.microsoft.com/dotnet/improving-multiplatform-container-support/
# 8.0-preview-alpine works too
FROM --platform=$BUILDPLATFORM mcr.microsoft.com/dotnet/sdk:8.0-preview AS build
ARG TARGETARCH
WORKDIR /source

# copy csproj and restore as distinct layers
COPY *.csproj .
RUN dotnet restore -a $TARGETARCH

# copy everything else and build app
COPY . .
RUN dotnet publish -a $TARGETARCH --no-restore -o /app


# final stage/image
FROM mcr.microsoft.com/dotnet/aspnet:8.0-preview

# Needed when csproj is .NET 7
ENV DOTNET_ROLL_FORWARD=Major
ENV DOTNET_ROLL_FORWARD_PRE_RELEASE=1

WORKDIR /app
COPY --from=build /app .

USER $APP_UID
ENTRYPOINT ["./dotnet-arm"]

dotnet-arm.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>

    <!-- We use SDK 8 to build, but the project can use .NET 7 or 6. -->
    <TargetFramework>net7.0</TargetFramework>
    <RootNamespace>dotnet_arm</RootNamespace>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>

</Project>

Program.cs

Console.WriteLine("Hello, World!");