How to Achieve Web Server Load Balancing and Data Sync with NFS on CentOS

Introduction

When traffic grows, a single web server may no longer suffice, requiring multiple servers and a method to keep their data synchronized. This article demonstrates how to achieve web server load balancing and data synchronization using NFS.

NFS Service Overview

NFS (Network File System) allows a system to share directories and files over a network, enabling users and programs to access remote files as if they were local. NFS relies on RPC for data transport.

Configuration Files on CentOS 6

Key packages and scripts:

Package: nfs-utils

Scripts: /etc/rc.d/init.d/nfs, /etc/rc.d/init.d/nfslock, /etc/rc.d/init.d/rpcgssd, /etc/rc.d/init.d/rpcidmapd, /etc/rc.d/init.d/rpcsvcgssd

Configuration files: /etc/exports, /etc/sysconfig/nfs

Export Options Explained

Common options include secure, rw, async / sync, no_wdelay, nohide, no_subtree_check, no_auth_nlm, mp, fsid, root_squash, no_root_squash, all_squash, anonuid, and anongid.

Useful Commands

showmount -e NFSSERVER_IP

mount -t nfs SERVER:/path/to/sharedfs /path/to/mount_point

exportfs -ar

exportfs -au

exportfs -u FS

vim /etc/fstab

Implementing NFS for Web Server Load Balancing

Workflow

Two web servers share the same WordPress site directory located on the NFS server at /web/blog. The DNS name blog.scholar.com resolves to both web servers.

Environment

DNS server: 172.168.10.10 (CentOS 6.6)

Web server 1: 172.16.10.100 (CentOS 6.6)

Web server 2: 172.16.10.212 (CentOS 6.6)

PHP server: 172.16.10.110 (CentOS 6.6)

NFS server: 172.16.10.110 (CentOS 6.6)

Database server: 172.16.10.211 (CentOS 6.6, MariaDB)

DNS Configuration

Configure forward and reverse zones for blog.scholar.com. (Images omitted for brevity.)

NFS Server Setup

Create the shared directory and set permissions.

Edit /etc/exports to export the directory to both web servers:

# vim /etc/exports

/web/blog 172.16.10.100(rw,sync) 172.16.10.212(rw,async)

Prepare WordPress Site

# unzip wordpress-3.2.1-zh_CN.zip

# cd wordpress

# mv * /web/blog

# cd /web/blog

# cp wp-config-sample.php wp-config.php

# vim wp-config.php

Set database credentials:

define('DB_NAME','wpdb');

define('DB_USER','wpuser');

define('DB_PASSWORD','wppass');

define('DB_HOST','172.16.10.211');

Database Server Configuration

Install and configure MariaDB for WordPress (image omitted).

Web Server Configuration

Enable required Apache modules:

# vim /etc/httpd24/httpd.conf

LoadModule proxy_module modules/mod_proxy.so

LoadModule proxy_fcgi_module modules/mod_proxy_fcgi.so

Enable virtual host:

# vim /etc/httpd24/extra/httpd-vhosts.conf

<VirtualHost *:80>

DocumentRoot "/web/blog"

ServerName blog.scholar.com

ProxyRequests Off

ProxyPassMatch ^/(.*\.php)$ fcgi://172.16.10.110:9000/web/blog/$1

<Directory "/web/blog">

Options none

AllowOverride none

Require all granted

</Directory>

</VirtualHost>

Mount Shared Directory on Web Servers

# vim /etc/fstab

172.16.10.110:/web/blog /web/blog nfs defaults,_netdev 0 0

Check syntax and start services (images omitted).

Testing

Access http://blog.scholar.com to verify the site loads. Publish a post on one web server and confirm it appears on the other, demonstrating successful data synchronization.

Conclusion

Using NFS to share the WordPress directory enables both web servers to serve the same site while keeping content synchronized, achieving load balancing without data inconsistency.