1 構建一個centos7.6.1810的docker鏡像，用於下載MySQL+xtrabackup所需安裝包

7.6.1810的docker鏡像，低版本最小安裝，會儘可能把所需的包拉齊。

Dockerfile文件如下

FROM centos:7.6.1810
 
CMD yum install -y https://repo.percona.com/yum/percona-release-latest.noarch.rpm https://repo.mysql.com//mysql80-community-release-el7-7.noarch.rpm epel-release && \
rm -rf /yum/mysql8.0 && mkdir -p /yum/mysql8.0 && \
yum --downloadonly --downloaddir=/yum/mysql8.0 install -y mysql-community-server percona-xtrabackup-80 zip unzip telnet lrzsz iotop ftp python-pip && \
yum-config-manager --disable mysql80-community && yum-config-manager --enable mysql57-community && \
rm -rf /yum/mysql5.7 && mkdir -p /yum/mysql5.7 && \
yum --downloadonly --downloaddir=/yum/mysql5.7 install -y mysql-community-server percona-xtrabackup-24 zip unzip telnet lrzsz iotop ftp python-pip

構建鏡像：

docker build -t mysql_xtrabackup_download .

2 運行鏡像自動下載MySQL5.7 / 8.0 + 對應版本的xtrabackup安裝包

docker run --rm \
  -v /etc/localtime:/etc/localtime \
  -v ${PWD}/yum:/yum \
  mysql_xtrabackup_download

docker容器跑完會自動銷毀，併在當前目錄的yum文件夾下生成mysql5.7 / mysql8.0兩個安裝包

傳輸到無網路的centos7上，可以使用yum localinstall *.rpm進行安裝

3 解決衝突

下載的rpm可以用於離線安裝，但是安裝時會報錯

新版本的MySQL已經不再提供libmysqlclient.so.18.1.0，但是xtrabackup需要這個文件，所以就有一個Percona-Server-shared-56-5.6.51-rel91.0.1.el7.x86_64.rpm包提供

這個包又提供了一個/etc/my.cnf文件，導致和MySQL主包衝突，無法安裝成功，所以要替換掉它。

Transaction check error:
  試圖安裝 mysql-community-server-8.0.31-1.el7.x86_64 和 Percona-Server-shared-56-5.6.51-rel91.0.1.el7.x86_64 會導致文件 /etc/my.cnf 衝突

下載Percona-Server-shared-56-5.6.51-rel91.0.1.el7.x86_64.rpm到Windows，解壓，得到兩個文件

 創建文件libmysqlclient.spec

Name:     libmysqlclient
Version:  18.1.0
Release:  1
Summary:  libmysqlclient-18.1.0
Summary(zh_CN):  libmysqlclient-18.1.0
License:  GPLv3+
 
Packager: XX Software
 
%description
libmysqlclient,Resolve MySQL and Xtrabackup installation conflicts
 
%description -l zh_CN
libmysqlclient，解決MySQL和xtrabackup安裝衝突
 
%install
mkdir -p %{buildroot}/usr/lib64
install -m 755 -t %{buildroot}/usr/lib64 /usr/lib64/libmysqlclient.so.18.1.0
install -m 755 -t %{buildroot}/usr/lib64 /usr/lib64/libmysqlclient_r.so.18.1.0
 
 
%files
/usr/lib64/libmysqlclient.so.18.1.0
/usr/lib64/libmysqlclient_r.so.18.1.0

創建文件Dockerfile

FROM centos:7.6.1810
 
RUN sed -e 's|^mirrorlist=|#mirrorlist=|g' \
        -e 's|^#baseurl=http://mirror.centos.org|baseurl=https://mirrors.tuna.tsinghua.edu.cn|g' \
        -i.bak \
        /etc/yum.repos.d/CentOS-*.repo && \
    yum install -y rpm-build rpmdevtools
 
CMD cd /tmp/libmysqlclient/ && \
    mkdir -p /usr/lib64 && \
    cp libmysqlclient*.so.18.1.0 /usr/lib64 && \
    rpmbuild -bb libmysqlclient.spec --define "_topdir ${PWD}/rpmbuild"

四個文件放同一個目錄，然後build + run

docker build -t rpm_libmysqlclient .
 
docker run --rm \
  -v /etc/localtime:/etc/localtime \
  -v ${PWD}:/tmp/libmysqlclient/ \
  rpm_libmysqlclient

最後會得到rpmbuild/RPMS/x86_64/libmysqlclient-18.1.0-1.x86_64.rpm包

替換掉Percona-Server-shared-56-5.6.51-rel91.0.1.el7.x86_64.rpm，再安裝就沒問題了。