R's Workshop

Clean APT Cache during Docker Image Build

以前就覺得 Docker image 很肥. 最近發現就算 Dockerfile 只有執行一行 apt update 也是會佔空間的!!!

舉個如下 Dockerfile 作為例子

FROM ubuntu:20.04
RUN apt update ;

$ docker build . -t temp

$ docker images
REPOSITORY                        TAG          IMAGE ID       CREATED          SIZE
temp                              latest       b105cc6751ec   5 minutes ago    105MB
ubuntu                            20.04        fb52e22af1b0   3 months ago     72.8MB

$ docker history temp:latest
IMAGE          CREATED              CREATED BY                                      SIZE      COMMENT
b105cc6751ec   About a minute ago   /bin/sh -c apt update ;                         31.9MB    
fb52e22af1b0   3 months ago         /bin/sh -c #(nop)  CMD ["bash"]                 0B        
<missing>      3 months ago         /bin/sh -c #(nop) ADD file:d2abf27fe2e8b0b5f…   72.8MB

Clean APT Cache

根據這份官方文件的說法, 原因是 apt update 後的 cache 佔了空間. 所以最好的作法是 apt install 完需要的 package 後, 把 APT cache 清掉.

$ rm -rf /var/lib/apt/lists/*

把上面的例子改成如下的 Dockerfile

FROM ubuntu:20.04
RUN apt update && rm -rf /var/lib/apt/lists/*

Docker build 出來後的 image 就可以發現 size 沒有增加了.

$ docker build . -t temp

$ docker images
REPOSITORY                        TAG          IMAGE ID       CREATED          SIZE
temp                              latest       afed09a38e9e   5 minutes ago    72.8MB
ubuntu                            20.04        fb52e22af1b0   3 months ago     72.8MB

$ docker history temp:latest
IMAGE          CREATED         CREATED BY                                      SIZE      COMMENT
afed09a38e9e   4 minutes ago   /bin/sh -c apt update  && rm -rf /var/lib/ap…   0B        
fb52e22af1b0   3 months ago    /bin/sh -c #(nop)  CMD ["bash"]                 0B        
<missing>      3 months ago    /bin/sh -c #(nop) ADD file:d2abf27fe2e8b0b5f…   72.8MB

不看說明書就開始玩遊戲果然是個壞習慣 (掩面) 找個時間來把這份官方文件讀完.

Reference

Docker Written on November 30th, 2021 by Borting
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