High Availability Linux Web Servers

If a web server goes down, here's one way to save time and minimize traffic loss by configuring multiple hosts to serve the same IP address.
Configuring Apache

Apache should be configured in /etc/conf/httpd.conf for Red Hat Linux to listen on each of the loopbacks that we've configured. Let's look at a simple example:

ServerName www.widgetco.com
DocumentRoot /www/www.widgetco.com

This tells Apache to listen on all four of our loopback interfaces, set the ServerName and set up the DocumentRoot from which Apache will provide content for www.widgetco.com. Though Apache will not see traffic on all four interfaces during normal operation, configuring Apache to listen beforehand will allow us to redirect traffic from one web server to another on the fly.

Redirecting Traffic

Redirecting traffic from one machine to another is fairly simple. It's just a matter of changing what your router thinks is the next hop for a given subnet or host. For example, if we need to reboot our first web server, we could redirect traffic to the second with the following Cisco router commands:

no ip route
ip route

All traffic that was going to is now rerouted to, the second web server, and we've dropped only the packets that were sent between the first and second router configuration commands. If your router is running Linux, you can write a simple shell script that changes these routes for you automatically. A few lines of Expect can change routes in a dedicated hardware router.

Other Applications?

This method of traffic redirection is not limited to web servers. Other applications using IP, and which could benefit from high availability, can utilize methods similar to the ones we've covered. A few examples include DNS, FTP and mail servers.

Aaron Gowatch is a Senior Systems Engineer living in San Francisco, California. These days he spends almost as much time wrenching on his Vespa and Lambretta motor scooters as he does sitting at the console. He can be reached at aarong@divinia.com.


One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems

As Linux continues to play an ever increasing role in corporate data centers and institutions, ensuring the integrity and protection of these systems must be a priority. With 60% of the world's websites and an increasing share of organization's mission-critical workloads running on Linux, failing to stop malware and other advanced threats on Linux can increasingly impact an organization's reputation and bottom line.

Learn More

Sponsored by Bit9

Linux Backup and Recovery Webinar

Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.

In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.

Learn More

Sponsored by Storix