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However, round robin DNS strategy solves this predicament, by mapping your domain name to more than one IP address.
Select hosting companies now employ DNS round robin technique in conjunction with'failover monitoring'.
The DNS round robin failover monitoring process starts by a web hosting company setting up your site on two or more independent web servers (preferably with different IP blocks assigned to them). Your domain name will therefore have 2 or more IP Addresses assigned to it.
Then failover monitor watches your web server(s) by dispatching data to a URL you specify and looking for particular text in results. When system detects that one of your IP addresses is returning an error, and others aren't, it pulls that IP address out of list. The DNS then points your domain name to working IP address/s
If any of your IP's come back online they are restored to IP pool. This effectively and safely keeps your site online – even if one of your web servers is down.
The average failure detection and recovery time with a system like this can be as low as 15 minutes. This time varies depending on speed of your site and nature of failure and also how long other ISP's cache (save) your DNS information.
The time taken for other ISP's caching your information can be manipulated in failover monitor by lowering "time to live" (TTL) cache settings. These are settings that other ISP's will use to determine how long to cache your DNS information.
Of course you must bear in mind matter of how frequently data is synchronized between your website's servers. This will be hosting company's responsibility, and this may become complicated where databases and user sessions are involved.
The very expensive hardware based failover monitoring systems that point a virtual IP address to other ISP's, while behind scenes juggling a number of unique IP addresses on different servers, is of course most 'elegant' solution to multi server hosting.
That way, whole issue of ISP's caching your information does not come into play.
Therefore, for site's that need to have true 99.99995% uptime, without huge outlays of money, technology is readily available and certain proprietory failure monitoring systems are now relatively cheap to apply.
Godfrey Heron is the Website Manager of the Irieisle Multiple Domain Hosting Services company.Signup for your free trial, and host multiple web sites on one account: http://www.irieisle-online.com