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This article describes the technology behind multiple server hosting and how you may utilize it to maximize your site's security and uptime. |
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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.
About The Author
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
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