Introduction
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Introduction
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24/7 continuous operation is critical when doing business on the Internet. Every minute your web site is not available, you loose sales and your good reputation! Unfortunately, web-servers are vulnerable to all kinds of disasters. Everything from simple power outages and disk drive failures to floods and earthquakes can quickly bring down your web site (and ruin you day). Failover systems can be used to protect against such outages. The definition of failover is when a user is automatically and transparently transferred from a failed system to a backup system, thereby ensuring uninterrupted operations. For example, when a web-server fails, and web-site visitors are automatically served by another standby web-server. Traditionally, failover functionality is performed on the network hardware level with specialized routers. Network data flow is switched between identical server computers (each configured with the same IP address). One serious limitation to this approach is that these server computers must be in the same physical location (within cabling range of the router), potentially making them vulnerable to the same disasters. Of course, the failover router itself also represents a potential single point of failure. Simple Failover is a software-based solution that uses a new and different approach to achieve the same goal. Instead of working on the network hardware level, it operates on the higher DNS level. All professional web sites today use domain names – such as http://www.simpledns.com. DNS servers are used to point each domain name to the numeric network address (IP address) of the corresponding web-server. Whenever you visit a web site, your computer must first consult with DNS to translate the domain name into an IP address, which is then used to communicate with the web-server. Simple Failover works by continuously testing the web-servers and dynamically updating DNS, so that a web-server domain name directs visitors to the IP address of a functional web-server. The web-server computers involved in this do not need to be in the same location, reducing vulnerability considerably. Multiple DNS server and Simple Failover installations can easily be setup for the same domain name eliminating any single point of failure. In fact, two simple computers in different locations, each running web-server software, DNS server software, and Simple Failover would practically eliminate the risk of any one disaster bringing down the web site. It is also entirely feasible to use a generic low-cost web-service as the backup, finally making failover protection available even to those with limited IT budgets. Simple Failover also provides basic server monitoring and status notification. This is similar to other "server monitoring" software solutions, with one significant difference: With monitoring-only software, you might get a message at 3AM reading:
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