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Advanced fault tolerant system: A more advanced system creates two active systems running simultaneously. In this active-active setup, any instance, or even an entire AZ can fail and the system will automatically be able to complete all its functions from another AZ that is pre-architected and ready to run on. RightScale says this architecture will cost more than double the cost of a single AZ setup, because all of the services form the single AZ not only have to be replicated, but there are data transfer costs that come with ensuring both systems are kept up-to-date in real time.
There are other options, too.
Sean Hull is an independent scalability and performance consultant with iHeavy in New York, and shortly after the AWS outage authored a blog post titled "AirBNB didn't have to fail," referring to the travel site that was one of dozens across the Internet that went down when AWS's cloud hiccupped. In the post, Hull argues there are tools Web developers can use to be tolerant against outages.
A website can be programmed to turn off certain features but keep the main part of the site up and running if parts of a system go down. In this case, someone browsing to the site would still be able to use basic functions of the site, but may not be able to make a purchase on the site. If a website is to be hosted at multiple locations, a browse-only mode could be active so that even if AWS does go out, a bare-bones version of the site is still accessible to users.
Other third-party vendors offer services within AWS's ecosystem for customers to create highly available systems. Amazon Web Services launched a marketplace of applications and services that have been optimized to run on AWS.
Customers can chose a variety of load balancers from one of these partners, such as Riverbed's Stingray division. Apurva Dave, VP of product marketing for the company, says there is a benefit to taking a "best of breed" approach of using third-party apps instead of simply relying on AWS for services such as load balancing.
"Have you ever been at an airport when a flight is canceled?" he says, as an analogy. "Everyone's in an immediate rush to get to the customer service desk and they wait in line. Then there are other folks, who just call their travel agent directly and the problem is taken care of. We're that travel agent that directs your traffic where it needs to go." Riverbed Stingray immediately and automatically redirects traffic over a dedicated network, avoiding the bottlenecks created in the AWS environment. Like the RightScale option, there are various levels of service that customers can choose from, ranging in price depending on how fault tolerant the system is.
As Hilgendorf says, and Dave agrees: It's a cost-benefit analysis for the business. "There are some apps where it's OK if it does down for an hour a month," Dave says. "But there are tons of apps that can't afford that."
Read more about cloud computing in Network World's Cloud Computing section.