Docker image 與 container 的建構流程

其實這張圖已經解說很清楚了

ARG

這裡有個 Dockerfile 範例如下 :

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ARG VERSION="latest"

FROM alpine:${VERSION}

ARG VERSION

RUN echo "alpine:${VERSION}" > /tmp/os_version

When building a docker image, you can overwrite ARG by using -–build-arg:

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$ docker build --build-arg VERSION=arg1_value

In docker-compose.yml file, it will look like :

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version: '3'

services:
  service1:
    build:
      context: ./dir-with-docker-compose
      args:
        arg1: arg1_value

When running a dokcer container, you can overwrite ENV by using -e :

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$ docker run -e "env1=env1_value" alpine env

In Dockerfile, it will look like :

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ENV VAR1 "Hello world"

RUN echo ${VAR1} > /tmp/demo

In docker-compose.yml file, it will look like :

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version: '3'

services:
  demo_alpine:
    image: alpine
      environment: 
        - env1=env1_value

Additionally, you can also use env-file to set massive envs :

demo_env.env

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env1=env1_value
env2=env2_value
env3=env3_value
env4=env4_value
env5=env5_value

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$ docker run --env-file=demo_env.env alpine env

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version: '3'

services:
  demo_alpine:
    image: alpine
      env_file: demo_env.env

舉一個例子

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FROM alpine

ARG VAR1="Hello world"
ENV VAR1 ${VAR1}

RUN echo ${VAR1} > /tmp/demo

Building image…

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$ docker build -t="demo-alpine" .

case 1

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$ docker run -e "VAR1=Hello Scott" demo-alpine env
HOSTNAME=f13f27da2cae
VAR1=Hello Scott
HOME=/root

列出環境變數，可透過 ENV 指定 VAR1 ，但 ARG 是不行的

case 2

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$ docker run -e "VAR1=Hello Scott" demo-alpine cat /tmp/demo
Hello world

在 Build image 階段，已經將 ARG 的值填入 /tmp/demo ，所以才會印出 Hello world

See different ?

That’s it !