为 WordPress 服务器添加 Memcached 支持

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在 WordPress 中开启 Memcached 缓存支持，可以加快网站访问速度。具体原理和配置请参考 WordPress 文档。本文着重介绍下在 Docker 方式部署的 WordPress 5.7 服务器上安装 Memcached 的方法步骤。

Docker 容器的 Linux 环境中包含一套 dpkg 和 apt 的包管理工具，所以如果在运维 Docker 部署的业务时临时需要用到什么软件，一般情况可以跟 Ubuntu 一样办法，使用 apt install 命令来安排常用软件。

先准备好一个 Docker 方式部署的 WordPress 网站实例。
进入 docker 容器的运行环境。

[root@ip-172-31-35-228 centos]# docker ps
CONTAINER ID   IMAGE              COMMAND                  CREATED      STATUS         PORTS                                   NAMES
4ce6a0bf360d   wordpress:latest   "docker-entrypoint.s…"   5 days ago   Up 5 days      0.0.0.0:8010->80/tcp, :::8010->80/tcp   ubuylogi_wordpress_1
b6bd40497f6f   mysql:5.7          "docker-entrypoint.s…"   5 days ago   Up 6 minutes   3306/tcp, 33060/tcp                     ubuylogi_ubuy_db_1
[root@ip-172-31-35-228 centos]# docker exec -it 4ce6a0bf360d /bin/bash
root@4ce6a0bf360d:/var/www/html# cd
root@4ce6a0bf360d:~# vim   
bash: vim: command not found

可以看到，vim 等一些常用的工具并不存在

直接用 apt-get update 更新源。

root@4ce6a0bf360d:~# apt update
Get:1 http://security.debian.org/debian-security bullseye-security InRelease [44.1 kB]
Get:2 http://deb.debian.org/debian bullseye InRelease [113 kB]                      
Get:3 http://deb.debian.org/debian bullseye-updates InRelease [36.8 kB]
Get:4 http://security.debian.org/debian-security bullseye-security/main amd64 Packages [29.4 kB]
Get:5 http://deb.debian.org/debian bullseye/main amd64 Packages [8178 kB]
Fetched 8401 kB in 2s (5057 kB/s)
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
1 package can be upgraded. Run 'apt list --upgradable' to see it.
root@4ce6a0bf360d:~#

先安装等下要用到的一些工具软件。apt install -y vim wget

root@4ce6a0bf360d:~# apt install -y vim wget
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  libgpm2 vim-common vim-runtime xxd
……

同样方法安装 zlib1g-dev 和 memcached

root@4ce6a0bf360d:~# apt install -y zlib1g-dev memcached
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
……

安装 memcached 后别忘了启动服务。

root@4ce6a0bf360d:~# /etc/init.d/memcached start
Starting memcached: memcached.
root@4ce6a0bf360d:~#

下载 libmemcached 并编译和安装（以下省略各命令的输出）。

root@4ce6a0bf360d:~# cd 
root@4ce6a0bf360d:~# wget https://launchpad.net/libmemcached/1.0/1.0.18/+download/libmemcached-1.0.18.tar.gz


root@4ce6a0bf360d:~# tar -zxvf libmemcached-1.0.18.tar.gz
root@4ce6a0bf360d:~# cd libmemcached-1.0.18
root@4ce6a0bf360d:~/libmemcached-1.0.18# ./configure --prefix=/usr/local/libmemcached --with-memcached
root@4ce6a0bf360d:~/libmemcached-1.0.18# make && make install
……

这一版 libmemcached 在我的环境中编译会出错，如下：

  CXX      clients/memflush.o
clients/memflush.cc: In function 'int main(int, char**)':
clients/memflush.cc:42:19: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   42 |   if (opt_servers == false)
      |       ~~~~~~~~~~~~^~~~~~~~
clients/memflush.cc:51:21: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   51 |     if (opt_servers == false)
      |         ~~~~~~~~~~~~^~~~~~~~
make[1]: *** [Makefile:5832: clients/memflush.o] Error 1
make[1]: Leaving directory '/root/libmemcached-1.0.18'
make: *** [Makefile:3700: all] Error 2
root@4ce6a0bf360d:~/libmemcached-1.0.18#

原因是 clients/memflush.cc 源文件中有两处指针类型变量与布尔型的对比操作，用vim打开源文件把false改为 NULL 再重新 make 即可。

接下来为 php 安装 memcached 插件

root@4ce6a0bf360d:~/libmemcached-1.0.18# pecl install memcached
pecl/memcached can optionally use PHP extension "igbinary" (version >= 2.0)
pecl/memcached can optionally use PHP extension "msgpack" (version >= 2.0)
downloading memcached-3.1.5.tgz ...
Starting to download memcached-3.1.5.tgz (83,015 bytes)
....................done: 83,015 bytes
15 source files, building
running: phpize
Configuring for:
PHP Api Version:         20190902
Zend Module Api No:      20190902
Zend Extension Api No:   320190902
libmemcached directory [no] : /usr/local/libmemcached
zlib directory [no] : 
use system fastlz [no] : 
enable igbinary serializer [no] : 
enable msgpack serializer [no] : 
enable json serializer [no] : 
enable server protocol [no] : 
enable sasl [yes] : no
enable sessions [yes] : 
building in /tmp/pear/temp/pear-build-defaultuser2i8dVo/memcached-3.1.5
……
Build process completed successfully
Installing '/usr/local/lib/php/extensions/no-debug-non-zts-20190902/memcached.so'
install ok: channel://pecl.php.net/memcached-3.1.5
configuration option "php_ini" is not set to php.ini location
You should add "extension=memcached.so" to php.ini
root@4ce6a0bf360d:~/libmemcached-1.0.18#

安装过程中，libmemcached 头文件路径填入上面 configure libmemcached 时指定的路径，zlib 头文件路径保持 no (pecl 自动检测），下面除了 sasl 改为 no 之外，其它都按默认。

libmemcached 安装完成后，需要从上一步输出的最后几行找到memcached so库的安装路径，填入 php 配置文件中。

root@4ce6a0bf360d:~# vim /usr/local/etc/php/php.ini

[Memcached]
extension_dir = "/usr/local/lib/php/extensions/no-debug-non-zts-20190902/"
extension = memcached.so

接下来可以确认一下 memcached 模块已经被 php 加载。（可能需要重启 php 服务）

root@bd570ad1c1a5:~/libmemcached-1.0.18# php -m | grep mem
memcached

最后重启 Docker 容器验证。如果以上步骤都执行成功，WordPress 的 object-cache.php 和 wp-config.php 文件也做了相应正确的设定，就可以在网站后台看到 Memcached 的缓存运行情况——包括命中率等数据的显示了。