如何从环境ARG中设置dockerfile中的WORKDIR？

Question

我想将WORKDIR /opt/app替换为全局ARG，但它不起作用：

ARG BUILD_IMAGE=maven:3.8.4-eclipse-temurin-11
ARG APP=/opt/app

FROM $BUILD_IMAGE as dependencies
#WORKDIR /opt/app #this would pass!
WORKDIR ${APP}

结果：

Error response from daemon: cannot normalize nothing
Failed to deploy Dockerfile': Can't retrieve image ID from build stream

为什么？

Answer 1

ARGs的作用域被限定到舞台，或者在文件顶部定义的from行。因此，在FROM行之后定义ARG，最好是在使用它之前(为了缓存效率)。

# define top level args used in FROM lines here
ARG BUILD_IMAGE=maven:3.8.4-eclipse-temurin-11

FROM $BUILD_IMAGE as dependencies
# define your args scoped within the stage after the FROM for that stage
ARG APP=/opt/app
WORKDIR ${APP}

如果您想设置一次arg值并重用它，则如下所示：

# define top level args used in FROM lines here
ARG BUILD_IMAGE=maven:3.8.4-eclipse-temurin-11
# the top section can also define the default value of an arg that is defined elsewhere
ARG APP=/opt/app

FROM $BUILD_IMAGE as dependencies
# define your args scoped within the stage after the FROM for that stage
ARG APP
WORKDIR ${APP}