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Problems
caused by growth are generally considered to be good problems to have. That
is, of course, unless your growing pains are affecting your website's
performance. If you're running serious business applications online, a slow
website equals lost dollars. This is true either directly--by missed sales
if you're running an e-commerce store--or indirectly--through lost customer
trust if you're providing a web-based solution to clients.
The
more important a website becomes to your operation, the less you can afford
to have slow performance or downtime. Snap decisions in crises, however, can
lead to greater expenses and more problems down the road. Many companies
will react under pressure of potentially lost revenue and sign up for or
internally implement a hosting solution that can handle the load, whether or
not that solution is right for their business in the long run.
So
how do you know which hosting solution is right for you? That depends
specifically on what you're trying to accomplish, and what's at stake.
Round
Robin DNS
Business owners looking to distribute load between two servers on the cheap
might implement a Round Robin DNS solution. In Round Robin DNS, traffic is
randomly distributed between two or more servers using DNS. This effectively
splits up a website's load, but the problem is that if one of the servers
goes down, half of your traffic will see the site as down. There's no
intelligence behind the load distribution.
Additional
problems may result if you're running a shopping cart or any other
session-based function on your site: If the network where your visitor is
originating from isn't caching DNS, you could find that they get shifted
between servers during a single session. While this won't happen in most
cases (since DNS caching is the norm), it would make filling out any
multiple-part forms, such as online order forms, impossible for those
visitors. This solution isn't recommended for most business uses because it
could cause more trouble than it saves you from.
Load
Balancing
Unlike Round Robin DNS, which randomly sends visitors to two different
servers, Load Balancing utilizes either a hardware switch or software to
intelligently direct traffic between two or more servers. Traffic can be
routed between servers based on which server has a lighter load. More
importantly, if one server goes down, a load-balancing solution can route
all traffic to the servers that are functioning properly.
Software
solutions such as Macromedia's ColdFusion ClusterCATS and the Windows 2003
Enterprise
operating system offer load balancing, but in my experience, a hardware
solution such as a Coyote Point Equalizer load balancer series operates more
efficiently. This is because the load balancing process runs on a separate
device from the servers, and thus doesn't generate additional overhead on
the servers. This is a good idea since the servers are probably pretty taxed
if a load balancing solution is under consideration in the first place.
Alternative
Web and Application Scaling Options
Another option that should be considered as an alternative to the two
solutions described above is this: If distributing load is the goal rather
than intelligent server failover, then splitting pieces of a website onto
different servers can be very effective.
Take,
for example, the instance of a business that's processing financial data
online. They may have two sets of users: one set that inputs market data,
and another set that runs reports on market data. By splitting the functions
that allow the inputting of market data onto one server, and the functions
that control report generation onto another server, their load can
effectively be split without having to invest in a load balancing solution.
Another nice benefit of this solution is that if one of the two servers
crashes, only one of the user groups will be impacted.
There's
also the option of keeping the code for both applications on each server. In
the case of a long server outage, this would allow you to activate the
downed application on the other application's server and run both
applications off one server until the downed server gets back online.
The
appeal of this method is that it distributes risk. If one part of your
site's down, other parts are still available for your customers to use. It's
not right for everyone, but it can be a good intermediate step for many
businesses. And with additional growth, one can always scale the individual
separated process to the load balancing framework as needed in the future.
Database
Replication
Setting up high-availability solutions for databases can be a bit more
complex than doing so for web and application servers. Database replication
used effectively can be an excellent, low-cost redundancy solution, whether
you're working with MySQL or Microsoft SQL databases. Database replication
copies data from one database (the master) to another (the slave), virtually
in real-time.
If
your primary database server crashes, you'll have a copy of your data on
another server. The key thing to understand is that replication won't
provide for automatic failover. Until you tell your web and application
servers to look at the secondary database server instead of the primary
database server, your database will be unavailable. However, making this
change is pretty easy to do, and you can have your database back online in
short order.
While
database replication is naturally only a redundancy solution, one can
fashion it into a high-availability solution to provide faster performance
for high-load sites. This can be done by having all database writes go to a
master, and all database reads come off of slave database servers. If
properly set up, this will effectively split the database load, and should
the master database server go down, one of the slaves can assume its place
with a few configuration changes.
Transaction
Log Shipping
In the Microsoft SQL world, transaction log shipping is an alternative to
replication. The main reason why one would use transaction log shipping is
because it puts the load of running the data transfer process on the server
receiving the data, rather than the server sending it. Since the server
sending the data is already under load as a live server that affects the
performance that your customers feel, moving the process to the secondary
server is beneficial (though the benefit may only be tangible under extreme
high-load conditions). The drawback of transaction log shipping is that it
only runs the data transfer process every 15 minutes, so a business that
uses this method risks up to a 15-minute loss of data.
Database
Clusters
Database Clusters, such as the Microsoft SQL Cluster model, offer failover
solutions for databases that can run automatically, as opposed to the
replication model described above that required manual intervention. Two or
more database servers share one common storage source, and should the
primary database server fail, the secondary one will take its place in a
heartbeat.
The
advantage to a system working this way is obvious: no lost data if the
primary database server crashes.
There
are two significant drawbacks, however. One is that performance can suffer
because the clustered servers can't utilize processor cache the way a single
server can; the primary server in the cluster must constantly be writing all
data to disk in case it fails and the secondary server needs to take over
for it. The other drawback is that further scaling the solution to handle
more load will incur exponential rather than linear costs.
In
my experience, database clusters are an excellent solution for low-volume
but mission-critical setups that require absolutely no downtime because the
performance difference won't be noticeable in such a scenario. For
businesses that require fast performance and redundancy, a better place to
look would be at the replication model described above that involves
splitting database reads between multiple slaves and database writes to a
master.
Conclusion
If proper forethought is given to growth before a snap decision is
necessary, businesses will save money and prevent headaches for their
customers--and for their employees who'll be tasked to solve the problem.
Although
the hosting solutions described above are great places to start, the right
growth plan for an individual business isn't something that can be
generalized in an article like this. It's something that should be developed
in consultation with an expert on hosting infrastructure, paying particular
attention to the needs and goals of the business in question.
Chris
Kivlehan is the marketing manager for INetU Managed Hosting. INetU is an
award-winning hosting provider that specializes in managed dedicated hosting
for businesses nationwide in the online retailing, web development,
e-learning, financial services and online marketing industries, as well as
for governments, non-profits and civic institutions.
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