AWS环境下WordPress多站点服务器横向扩展方案咨询

Hey there! Let's walk through exactly how to scale your WordPress Multisite setup horizontally by adding a second identical server. I've handled this scenario a few times, so here's a step-by-step breakdown that covers all critical pieces:

First, make sure you've got the basics covered to avoid mismatches down the line:

• Ensure both servers are identical: same OS version, PHP version, web server (Apache/Nginx), WordPress core version, and all installed plugins/themes.
• Full backup of your existing server: export the entire WordPress Multisite database, copy the wp-content directory (uploads, themes, plugins), and save config files like wp-config.php and .htaccess.

Since Multisite relies on shared media, themes, and plugins, you can't have separate wp-content folders on each server:

• Deploy a shared storage solution (NFS or SMB work well) and migrate your existing wp-content directory to this shared location.
• Mount the shared storage to /var/www/html/wp-content (or your WordPress root's wp-content path) on both servers.
• Verify web server permissions: run sudo chown -R www-data:www-data /var/www/html/wp-content to ensure the server user can read/write to the shared folder.

WordPress Multisite needs a single shared database to sync sites, users, and settings across servers:

• Export your existing Multisite database: mysqldump -u [db-username] -p [multisite-db-name] > multisite-backup.sql
• Set up a database server (can be a standalone instance or one of your web servers, but standalone is better for scalability) and create a database user that's authorized to access from both web server IPs.
• Import the backup to the shared database on your second server: mysql -u [db-username] -p [multisite-db-name] < multisite-backup.sql
• Update wp-config.php on both servers to point to the shared database: ensure DB_HOST, DB_NAME, DB_USER, and DB_PASSWORD are identical, along with all Multisite-specific defines (like WP_ALLOW_MULTISITE, DOMAIN_CURRENT_SITE, and PATH_CURRENT_SITE).

You need a way to distribute traffic across both servers—here's how to handle it:

• Choose a load balancer: Nginx (as a reverse proxy), HAProxy, or a cloud-native LB (like AWS ALB) all work.
• Configure the LB to route traffic to both web server IPs, and set up health checks (e.g., pinging a static file or /wp-admin/install.php to verify server availability).
• Fix session consistency: WordPress uses PHP sessions, so you have two options:
  • Preferred: Use shared session storage (Redis or Memcached). Install the Redis PHP extension, then add these lines to wp-config.php on both servers:

    define('WP_REDIS_HOST', 'your-redis-server-ip');
    define('WP_REDIS_PORT', 6379);
    define('SESSION_SAVE_HANDLER', 'redis');
    define('SESSION_SAVE_PATH', 'tcp://your-redis-server-ip:6379?database=0');
    

  • Sticky sessions (fallback): Configure your LB to route a user's traffic to the same server for their session, but note this reduces load-balancing efficiency.

Make sure both servers handle traffic the same way:

• Copy your existing web server config (e.g., Apache's /etc/apache2/sites-available/wordpress.conf or Nginx's /etc/nginx/sites-available/wordpress.conf) to the second server.
• Double-check paths and domain names in the config (since wp-content is shared, paths should match exactly).
• Restart the web server on both instances: sudo systemctl restart apache2 or sudo systemctl restart nginx.

Don't skip this step—verify everything works as expected:

• Visit your site via the load balancer's domain to confirm it loads correctly.
• Upload a test media file, then check the shared storage to ensure it's accessible from both servers.
• Log into wp-admin, create a test subsite, and verify it appears when accessing the site via either server directly.
• Test failover: Stop one web server and confirm traffic automatically routes to the remaining server without downtime.

To keep both servers aligned long-term:

• Use Git to track and sync config files like wp-config.php and web server settings.
• Set up an automation tool like Ansible to push configuration changes to both servers at once, eliminating manual updates.

内容的提问来源于stack exchange，提问作者VIJAY THAKUR