#92;--no-cache Vs的Alpine Dockerfile的优势 rm / var / cache / apk / *
该--no-cache选项允许不在本地缓存索引，这对于保持容器较小非常有用。
从字面上看，它apk update在开头和rm -rf /var/cache/apk/*结尾相等。
我们使用--no-cacheoption的一些示例：
$ docker run -ti alpine:3.7
/ # apk add Nginx
WARNING: Ignoring APKINDEX.70c88391.tar.gz: No such file or directory
WARNING: Ignoring APKINDEX.5022a8a2.tar.gz: No such file or directory
ERROR: unsatisfiable constraints:
Nginx (missing):
required by: world[Nginx]
/ #
/ # apk add --no-cache Nginx
fetch http://dl-cdn.alpinelinux.org/alpine/v3.7/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.7/community/x86_64/APKINDEX.tar.gz
(1/2) Installing pcre (8.41-r1)
(2/2) Installing Nginx (1.12.2-r3)
Executing Nginx-1.12.2-r3.pre-install
Executing busyBox-1.27.2-r7.trigger
OK: 6 MiB in 13 packages
/ #
/ # ls -la /var/cache/apk/
total 8
drwxr-xr-x 2 root root 4096 Jan 9 19:37 .
drwxr-xr-x 5 root root 4096 Mar 5 20:29 ..
另一个不使用--no-cache选项的示例：
$ docker run -ti alpine:3.7
/ # apk add Nginx
WARNING: Ignoring APKINDEX.70c88391.tar.gz: No such file or directory
WARNING: Ignoring APKINDEX.5022a8a2.tar.gz: No such file or directory
ERROR: unsatisfiable constraints:
Nginx (missing):
required by: world[Nginx]
/ #
/ # apk update
fetch http://dl-cdn.alpinelinux.org/alpine/v3.7/main/x86_64/APKINDEX.tar.gz
fetch http://dl-cdn.alpinelinux.org/alpine/v3.7/community/x86_64/APKINDEX.tar.gz
v3.7.0-107-g15dd6b8ab3 [http://dl-cdn.alpinelinux.org/alpine/v3.7/main]
v3.7.0-105-g4b8b158c40 [http://dl-cdn.alpinelinux.org/alpine/v3.7/community]
OK: 9048 distinct packages available
/ #
/ # apk add Nginx
(1/2) Installing pcre (8.41-r1)
(2/2) Installing Nginx (1.12.2-r3)
Executing Nginx-1.12.2-r3.pre-install
Executing busyBox-1.27.2-r7.trigger
OK: 6 MiB in 13 packages
/ #
/ # ls -la /var/cache/apk/
total 1204
drwxr-xr-x 2 root root 4096 Mar 5 20:31 .
drwxr-xr-x 6 root root 4096 Mar 5 20:31 ..
-rw-r--r-- 1 root root 451508 Mar 3 00:30 APKINDEX.5022a8a2.tar.gz
-rw-r--r-- 1 root root 768680 Mar 5 09:39 APKINDEX.70c88391.tar.gz
/ #
/ # rm -vrf /var/cache/apk/*
removed '/var/cache/apk/APKINDEX.5022a8a2.tar.gz'
removed '/var/cache/apk/APKINDEX.70c88391.tar.gz'
如您所见，这两种情况都是有效的。对我来说，使用--no-cacheoption更为优雅。
解决方法
使用Alpine映像创建Dockerfile时，我经常看到apk --no-cache提交时使用和的用法，而是看到rm /var/cache/apk/*。
我很好奇，知道利用--no-cache消除了以后再做的必要rm /var/cache/apk/*。我还想知道一种风格是否胜过另一种。
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