优化Docker中.NET构建：Publish阶段为何重复编译？能否跳过Build？

我有一个Rider生成的Dockerfile，内容如下：

FROM mcr.microsoft.com/dotnet/runtime:7.0 AS base
WORKDIR /app

FROM mcr.microsoft.com/dotnet/sdk:7.0 AS build
WORKDIR /src
COPY ["Services/AnalyzerHistory/AnalyzerHistory.fsproj", "Services/AnalyzerHistory/"]
RUN dotnet restore "Services/AnalyzerHistory/AnalyzerHistory.fsproj"
COPY . .
WORKDIR "/src/Services/AnalyzerHistory"
RUN dotnet build "AnalyzerHistory.fsproj" -c Release -o /app/build

FROM build AS publish
RUN dotnet publish "AnalyzerHistory.fsproj" -c Release -o /app/publish

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

构建日志显示Build阶段完成后，Publish阶段又重新编译了所有内容，导致构建时间翻倍：

#13 [build 7/7] RUN dotnet build "AnalyzerHistory.fsproj" -c Release -o /app/build
#13 0.425 MSBuild version 17.7.3+4fca21998 for .NET
#13 1.423   Determining projects to restore...
#13 3.952   Restored /src/Credentials/Credentials.fsproj (in 551 ms).
...
#13 49.47   AnalyzerHistory -> /app/build/AnalyzerHistory.dll
#13 49.52 Build succeeded.
#13 49.52 Time Elapsed 00:00:48.84
#13 DONE 49.8s

#14 [publish 1/1] RUN dotnet publish "AnalyzerHistory.fsproj" -c Release -o /app/publish
#14 0.667 MSBuild version 17.7.3+4fca21998 for .NET
#14 1.519   Determining projects to restore...
#14 3.503   All projects are up-to-date for restore.
#14 8.960   Credentials -> /src/Credentials/bin/Release/net7.0/Credentials.dll
...
#14 41.72   AnalyzerHistory -> /src/Services/AnalyzerHistory/bin/Release/net7.0/AnalyzerHistory.dll
#14 41.80   AnalyzerHistory -> /app/publish/
#14 DONE 42.0s

我不理解为何Publish阶段会重复编译，这似乎让构建时间增加了一倍。请问我是否可以跳过Build阶段，直接使用Publish？

为什么Publish阶段会重复编译 #

dotnet publish 默认会先执行build目标，但你的Build阶段把输出放到了/app/build，而Publish阶段默认读取项目目录下的bin/Release目录作为中间输出，两者路径不匹配，导致Publish阶段无法复用Build阶段的编译结果，只能重新执行编译流程。

可以跳过Build阶段吗？ #

完全可以，这是优化构建时间的合理方案。dotnet publish本身就包含了restore和build的完整流程，不需要单独执行build步骤。你可以直接合并Build和Publish阶段，简化Dockerfile：

优化后的Dockerfile #

FROM mcr.microsoft.com/dotnet/runtime:7.0 AS base
WORKDIR /app

FROM mcr.microsoft.com/dotnet/sdk:7.0 AS publish
WORKDIR /src
COPY ["Services/AnalyzerHistory/AnalyzerHistory.fsproj", "Services/AnalyzerHistory/"]
RUN dotnet restore "Services/AnalyzerHistory/AnalyzerHistory.fsproj"
COPY . .
WORKDIR "/src/Services/AnalyzerHistory"
RUN dotnet publish "AnalyzerHistory.fsproj" -c Release -o /app/publish

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

保留分层构建的优化方案（可选） #

如果希望保留Build阶段的缓存优势（比如后续仅修改代码时，restore步骤可以复用缓存），可以让Build阶段的输出路径与Publish阶段的默认路径对齐，或者在publish时指定使用Build阶段的输出：

FROM mcr.microsoft.com/dotnet/runtime:7.0 AS base
WORKDIR /app

FROM mcr.microsoft.com/dotnet/sdk:7.0 AS build
WORKDIR /src
COPY ["Services/AnalyzerHistory/AnalyzerHistory.fsproj", "Services/AnalyzerHistory/"]
RUN dotnet restore "Services/AnalyzerHistory/AnalyzerHistory.fsproj"
COPY . .
WORKDIR "/src/Services/AnalyzerHistory"
# 构建到默认的bin/Release目录，让publish可以复用结果
RUN dotnet build "AnalyzerHistory.fsproj" -c Release

FROM build AS publish
# 使用--no-build参数，直接复用build阶段的编译结果
RUN dotnet publish "AnalyzerHistory.fsproj" -c Release -o /app/publish --no-build

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

这里的核心是通过--no-build参数告诉dotnet publish跳过编译步骤，直接使用已有的构建结果，同时确保Build阶段的输出路径符合Publish阶段的预期。

内容的提问来源于stack exchange，提问作者Thomas