使用 ARG
可以有效的复用 Dockerfile。每次镜像更新,只需要动态的在 build
命令中传入新的参数值即可。
FROM
之前的所有 ARG , 在所有 FROM
中生效, 仅在 FROM
中生效FROM
后的 ARG
, 仅在当前 FROM
作用域生效。即尽在当前 阶段 (stage) 生效在随后的 Dockerfile 中, 只定义了一个变量 image
, 并在 FROM
和 stage 中重复使用
stage1
和 stage11
均在 FROM
中使用了变量 $image
: **作用域在所有 FROM
中FROM $image
并完成 layer 构建RUN
中无法正确输出结果,即 image 的值 alpine:3.12stage1
vs stage2
: 作用域在 FROM stage 内部stage2
的作用域中声明了 ARG image
,且能正确输出结果。stage2
vs stage21
: 作用域仅在当前 FROM stage
内部stage2
在 stage21
上方且声明了 ARG image
, 但 stage21
仍然不能不能正确输出结果。
## 在第一个 FROM 之前的所有 ARG , 在所有 FROM 中生效, 仅在 FROM 中生效
ARG image
FROM $image as stage1
RUN echo "stage1 -> base from image is : $image "
# result: stage1 -> base from image is :
FROM $image as stage11
RUN echo "stage11 -> base from image is : $image "
# result: stage11 -> base from image is :
FROM alpine:3.12 as stage2
## 在 FROM 后的 ARG, 仅在当前 FROM 作用域生效。即尽在当前 阶段 (stage) 生效
ARG image
RUN echo "stage2 -> base from image is : $image "
# stage2 -> base from image is : alpine:3.12
FROM alpine:3.12 as stage21
RUN echo "stage21 -> base from image is : $image "
# stage21 -> base from image is :
docker build
命令# docker build --build-arg image=alpine:3.12 --no-cache .
build
结果展示Sending build context to Docker daemon 3.072kB
Step 1/10 : ARG image
Step 2/10 : FROM $image as stage1
---> d6e46aa2470d
Step 3/10 : RUN echo "stage1 -> base from image is : $image "
---> Running in ecb7be5dd9cc
stage1 -> base from image is : ### image 结果未输出
Removing intermediate container ecb7be5dd9cc
---> 04807c8d53be
Step 4/10 : FROM $image as stage11
---> d6e46aa2470d
Step 5/10 : RUN echo "stage11 -> base from image is : $image "
---> Running in a90e45076345
stage11 -> base from image is : ### image 结果未输出
Removing intermediate container a90e45076345
---> f2dbce837a1b
Step 6/10 : FROM alpine:3.12 as stage2
---> d6e46aa2470d
Step 7/10 : ARG image
---> Running in 5c8cec4c2f22
Removing intermediate container 5c8cec4c2f22
---> 999d9990bd91
Step 8/10 : RUN echo "stage2 -> base from image is : $image "
---> Running in 4407dcb0e0bb
stage2 -> base from image is : alpine:3.12 ### image 结果输出
Removing intermediate container 4407dcb0e0bb
---> e5ddd7a84f81
Step 9/10 : FROM alpine:3.12 as stage21
---> d6e46aa2470d
Step 10/10 : RUN echo "stage21 -> base from image is : $image "
---> Running in 64a0a3bb090c
stage21 -> base from image is : ### image 结果未输出
Removing intermediate container 64a0a3bb090c
---> 82665f9a1037
Successfully built 82665f9a1037
0x04 to be continue
在以后的时间, 笔者将继续讨论 ARG 在 docker buildx 多节构建时的影响和使用。