如何解决 CentOS 7 官方 yum 仓库无法使用

一、背景介绍

编译基于 CentOS 7.6.1810 镜像的 Dockerfile 过程中，执行 yum install 指令时，遇到了错误：Could not resolve host: mirrorlist.centos.org; Unknown error。

 二、原因分析

官方停止维护 CentOS 7。该系统内置的 yum.repo 所使用的域名 mirrorlist.centos.org 已不再提供 A 记录。如下所示：

root@93b1bbdc2e60:/home/# dig mirrorlist.centos.org +trace

; <<>> DiG 9.16.1-Ubuntu <<>> mirrorlist.centos.org +trace
;; global options: +cmd
.                       0       IN      NS      c.root-servers.net.
.                       0       IN      NS      i.root-servers.net.

## 省略：根和顶级域名服务器的相关解析

centos.org.             3600    IN      NS      ns1.centos.org.
centos.org.             3600    IN      NS      ns2.centos.org.
gdtpongmpok61u9lvnipqor8lra9l4t0.org. 3600 IN NSEC3 1 1 0 332539EE7F95C32A GDTREA8KMJ2RNEQEN4M2OGJ26KFSUKJ7 NS SOA RRSIG DNSKEY NSEC3PARAM
qeunu2n7u9cespp9113b9aougs8bsje9.org. 3600 IN NSEC3 1 1 0 332539EE7F95C32A QEUO6270NIE81LB4QN59HMMDKF8L01MV NS DS RRSIG
gdtpongmpok61u9lvnipqor8lra9l4t0.org. 3600 IN RRSIG NSEC3 8 2 3600 20240730022208 20240709012208 36783 org. SJRvhqxd780LYLBKJvh+HK1XHVN4Jm3FReq030r3Aewe0Sus1xpbl7L9 xOJOudja1lZoBdgfVXFBQT4Ev9M6XSG6c9qYJvDT9Q9U8PQyG+KDGGTy zTNgK1QFgFM7Sq1DPiqeUc5Jc/mmD7H26TV2qrCem4Fz8/TYYlK9CirT VKU=
qeunu2n7u9cespp9113b9aougs8bsje9.org. 3600 IN RRSIG NSEC3 8 2 3600 20240722152150 20240701142150 36783 org. wq21TFtc5dCtXghEDYN+dJLnZUiJzzcoVLIWQ2aA5FCIV/pHKfUPg7Mn jXjOGMK5Xx8lu7gBjdKvu7yQaVrlEJXC0wo8QqzlrB/yL6EcBhypBfNk b+vH7RCfrfOsIqwMKCv82wF91/S4/3uVijxeD2F+nEjvPLJheRQcxQR1 r/g=
;; Received 619 bytes from 199.249.120.1#53(b2.org.afilias-nst.org) in 179 ms

centos.org.             3600    IN      SOA     ns1.centos.org. hostmaster.centos.org. 2024070401 28800 7200 2400000 3600
;; Received 129 bytes from 38.145.60.38#53(ns2.centos.o