How Multiple Server Hosting impacts your website`s uptime

How Multiple Server Hosting impacts your website`s
uptime
By Godfrey E. Heron

This article describes the technology behind multiple server
hosting and how you may utilize it to maximize your site`s
security and uptime

Hosting of web sites has essentially become a commodity. There
is very little distinguishing one hosting company from the
next. Core plans and features are the same and price is no
longer a true determining feature. In fact, choosing a host
based on the cheapest price can be more expensive in the long
term with respect to reliability issues and possible loss of
sales as a result of website downtime.

Selecting a host from the thousands of providers and resellers
can be a very daunting task, which may result in a hit and
miss approach. But although hosting may have become a
commodity, one distinguishing feature that you must always
look out for is reliability.

At the heart of any hosting company`s reliability is redundancy.
This ensures that if a problem exists at one point, there
will be an alternative which ensures continuity as seemlessly
and transparently as possible.

Most hosts do employ redundant network connections. These are
the high speed pipes that route data from the server to your
web browser. But, redundant `multiple web servers` have been
extremely rare and very expensive, requiring costly routing
equipment which has previously been used only in mission
critical applications of Fortune 500 companies.

However, a very neat but little known Domain Name Server(DNS)
feature called `round robin` allows the selection and
provision of a particular IP address from a `pool` of
addresses when a DNS request arrives.

To understand what this has to do with server reliability it`s
important to remember that the Domain Name Server (DNS)
database maps a host name to their IP address. So instead of
using a hard to remember series of numbers (IP address) we
just type in your web browser www.yourdomain.com, to get to
your website.

Now, typically it takes at at least 2 to 3 days to propagate or
‘spread the word’ of your DNS info throughout the internet.
That`s why when you register or transfer a domain name it
isn`t immediately available to the person browsing the web.

This delay has stymied the security benefits of hosting your
site on multiple servers, as your site would be down for a
couple of days if something went awry with one server. You
would have to change your DNS to reflect your second server
and wait days before the change was picked up in routers on
the internet.

However, the round robin DNS strategy solves this predicament,
by mapping your domain name to more than one IP address.

Select hosting companies now employ the 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 the failover monitor watches your web server(s) by
dispatching data to a URL you specify and looking for
particular text in the results. When the system detects that
one of your IP addresses is returning an error, and the others
aren`t, it pulls that IP address out of the list. The DNS then
points your domain name to the working IP address/s

If any of your IP`s come back online they are restored to the
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 the speed of your site and the nature of the
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 the failover monitor by lowering the "time to
live" (TTL) cache settings. These are the settings that other
ISP`s will use to determine how long to cache your DNS
information.

Of course you must bear in mind the matter of how frequently
data is synchronized between your website`s servers. This will
be the 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
the scenes juggling a number of unique IP addresses on
different servers, is of course the most `elegant` solution to
multi server hosting.

That way, the 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, the technology is readily
available and certain proprietory failure monitoring systems
are now relatively cheap to apply.

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