如何在Laravel Framework6.0中启用主从？

DB_HOST=主数据库地址
DB_PORT=主数据库端口
DB_DATABASE=主数据库名称
DB_USERNAME=主数据库用户名
DB_PASSWORD=主数据库密码

DB_CONNECTION_SLAVE=mysql
DB_HOST_SLAVE=从数据库地址
DB_PORT_SLAVE=从数据库端口
DB_DATABASE_SLAVE=从数据库名称
DB_USERNAME_SLAVE=从数据库用户名
DB_PASSWORD_SLAVE=从数据库密码

<?php

return [
    'default' => env('DB_CONNECTION_SLAVE', 'mysql'),
    'connections' => [
        'mysql' => [
            'driver' => 'mysql',
            'host' => env('DB_HOST_SLAVE', '127.0.0.1'),
            'port' => env('DB_PORT_SLAVE', '3306'),
            'database' => env('DB_DATABASE_SLAVE', 'forge'),
            'username' => env('DB_USERNAME_SLAVE', 'forge'),
            'password' => env('DB_PASSWORD_SLAVE', ''),
            'charset' => 'utf8mb4',
            'collation' => 'utf8mb4_unicode_ci',
            'prefix' => '',
            'strict' => true,
            'engine' => null,
        ],
    ],
];

'mysql' => [
    'driver' => 'mysql',
    'host' => env('DB_HOST', '127.0.0.1'),
    'port' => env('DB_PORT', '3306'),
    'database' => env('DB_DATABASE', 'forge'),
    'username' => env('DB_USERNAME', 'forge'),
    'password' => env('DB_PASSWORD', ''),
    'charset' => 'utf8mb4',
    'collation' => 'utf8mb4_unicode_ci',
    'prefix' => '',
    'strict' => true,
    'engine' => null,
],

'mysql' => [
    'driver' => 'mysql',
    'read' => [
        'host' => [
            '主数据库地址',
        ],
    ],
    'write' => [
        'host' => [
            '主数据库地址',
        ],
    ],
    'sticky' => true,
    'host' => [
        '主数据库地址',
    ],
    'port' => env('DB_PORT', '3306'),
    'database' => env('DB_DATABASE', 'forge'),
    'username' => env('DB_USERNAME', 'forge'),
    'password' => env('DB_PASSWORD', ''),
    'charset' => 'utf8mb4',
    'collation' => 'utf8mb4_unicode_ci',
    'prefix' => '',
    'strict' => true,
    'engine' => null,
],

$users = DB::connection('mysql')->select('select * from users');