读写分离, laravel会自动将"read"的操作向read服务器，"write"的访问write服务器
https://laravel.com/docs/5.5/database#configuration

// config/database.php 配置读写，下面是2台读服务器，1台写
'mysql' => [
    'read' => [
        ['host' => '192.168.10.1','password'=>env('DB_READ_PWD1')],
        ['host' => '192.168.10.2','password'=>env('DB_READ_PWD2')],
    ],
    'write' => [
        'host' => '196.168.10.2'
    ],
    'sticky'    => true,
    'driver'    => 'mysql',
    'database'  => 'database',
    'username'  => 'root',
    'password'  => 'passwd',
    'charset' => 'utf8mb4',
    'collation' => 'utf8mb4_unicode_ci',
    'prefix'    => '',
],