.NET 7多平台Docker构建：如何在Dockerfile中条件设置目标平台？

问题核心是Docker的每个RUN指令都会启动独立的shell进程，进程内定义的变量无法跨RUN指令保留。针对你的场景，提供两种简洁的解决方式：

方式一：合并命令到同一个RUN指令 #

将变量判断、dotnet restore和dotnet publish放在同一个RUN中，利用shell会话内的变量有效性完成配置：

FROM mcr.microsoft.com/dotnet/sdk:7.0 AS build-env

ARG TARGETPLATFORM
ARG BUILDPLATFORM

RUN echo "I am running on $BUILDPLATFORM, building for $TARGETPLATFORM" > /log

WORKDIR /app
COPY . ./

# 条件判断与构建命令合并，变量在当前shell会话中有效
RUN if [ "$TARGETPLATFORM" = "linux/arm64" ]; then \
        DOTNET_TARGET=linux-musl-arm64; \
    else \
        DOTNET_TARGET=linux-x64; \
    fi && \
    dotnet restore MyApp -r $DOTNET_TARGET /p:PublishReadyToRun=true && \
    dotnet publish MyApp -c Release -o Ahs.AuthManager/out -r $DOTNET_TARGET --self-contained true --no-restore /p:PublishTrimmed=true /p:PublishReadyToRun=true /p:PublishSingleFile=true

## more to follow here...

注意：原代码中"linux/arm64 "多了一个空格，需删除才能正确匹配目标平台。

方式二：使用ARG预定义目标RID #

通过ARG定义目标RID参数，结合shell命令将TARGETPLATFORM映射为对应的.NET RID，后续指令直接引用该参数：

FROM mcr.microsoft.com/dotnet/sdk:7.0 AS build-env

ARG TARGETPLATFORM
ARG BUILDPLATFORM
# 默认目标平台为linux-x64
ARG DOTNET_TARGET=linux-x64

RUN echo "I am running on $BUILDPLATFORM, building for $TARGETPLATFORM" > /log && \
    # 根据TARGETPLATFORM更新DOTNET_TARGET的值
    if [ "$TARGETPLATFORM" = "linux/arm64" ]; then \
        echo "DOTNET_TARGET=linux-musl-arm64" > /tmp/target_config; \
    fi

# 将配置文件中的变量导入当前环境，供后续构建命令使用
WORKDIR /app
COPY . ./
RUN export $(cat /tmp/target_config 2>/dev/null) && \
    dotnet restore MyApp -r $DOTNET_TARGET /p:PublishReadyToRun=true && \
    dotnet publish MyApp -c Release -o Ahs.AuthManager/out -r $DOTNET_TARGET --self-contained true --no-restore /p:PublishTrimmed=true /p:PublishReadyToRun=true /p:PublishSingleFile=true

## more to follow here...

这种方式适合需要在多个RUN指令中复用目标平台参数的场景，通过临时文件传递变量值。

内容的提问来源于stack exchange，提问作者silent