Expectations of Availability in the Cloud

Posted: 05/01/2013
By: Andrew H.

Does “Availability” Mean “Always On”?

Yep, these days, they are pretty much the same thing. The promise that your hosting network, platform, or service will be there when anyone accesses it, anytime—whether it’s you, your staff, your customers—that’s high availability (HA). It’s a percentage that represents a system’s expected uptime, or availability, over a given period, preferably with several nines present: 99.9%, 99.95%--you get the idea.

From a consumer’s point of view, the Internet doesn’t have business hours. It’s always there, always on, always ready. But we all know that’s not realistically the case. Failed hardware, natural disasters, a worker throwing the wrong switch, and software updates can all cause temporary network outages.

Can you trust the cloud to come through? Yes, because the resilience of clustering technology and the distributed nature of the cloud helps absorb and avoid the bumps on the Internet highway. How do cloud providers keep your cloud-based infrastructure, platforms, and software available and ready?

Fail-over: The Key To High Availability in the Cloud

Fail-over means that when a system stops working for whatever reason, another system jumps in. Cloud providers typically achieve this through clustering, where multiple servers continually monitor each other and replicate data. In the event a server fails, another one takes over. Good cloud providers constantly check hardware systems for signs that a failure might occur, and test their fail-over systems to ensure they work as expected. Now, clustering can provide very high levels of availability, but it can’t guarantee 100% uptime—even 99.95% works out to being offline a little over 4 hours a year. However, fail-over is generally rapid, and might require a few seconds to a few minutes to occur depending on the solution in place.

Network Availability: How Many Nines Do You Need?

For some industries like air traffic control, fully redundant systems are necessary, but they are typically very expensive, and entail creating and maintaining duplicate systems that wait silently to take over (and sit idle the rest of the time).

For many businesses, the HA provided by clustering and other solutions is more than enough.  As to how many nines you need for your network availability that will depend on several factors. Take a look at how your business operates and study how much a given amount of downtime actually costs. Knowing that information will help the most in guiding your decision.

The cloud is the right place to be. After you know what you really need, what you can tolerate, and what the costs are, then you can ask the right questions of a cloud services provider and match your needs to the right package for you and your business.

How does your business determine the level of availability it needs? Are you getting the availability that you expect? If not, why not? Tell us!

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