Each customer has to do his own risk assessment to determine how much should be invested to ensure high availability of services, Hendrick says. Having copies of data across multiple availability zones can increase costs of using AWS's cloud, he says, perhaps by as much as 50 percent. "I don't know how many enterprises really appreciate what high availability means," he says. A rule of thumb is that the more mission-critical applications and data in the cloud are, the more attention customers should pay to architecting for high availability. For some customers, just a multi-AZ approach isn't enough. "We always store data in multiple zones to avoid [outages]," Jeremy Edberg, senior product developer at Reddit was quoted as saying last year. "The reason it went down is that it failed in multiple zones."
A strategy that goes beyond using a multi-AZ approach within the AWS ecosystem involves storing data across regions, says Reeves, the Gartner analyst. This can be somewhat more complicated because while AWS allows for common APIs between AZs within a single region, separate API calls are needed for using multiple regions. This is the approach Quora has taken since last year's outage. On the question-and-answer social media site, a Quora engineer notes that the company is using a "cross region database replication" strategy to distribute its content.
There are nontechnical steps customers can take as well, Reeves says. Customers can negotiate with providers to guarantee availability and stipulate consequences for not meeting those in service-level agreements (SLA). In AWS's outage case, any customers using the impacted availability zone received a 10-day credit, regardless of whether they experienced downtime.
Still though, there will always be risks and outages, and in a way, Reeves says that's a good thing: It keeps companies and end users on their toes. "I really believe that outages can propel the cloud further rather than hinder it," he says. "If we learn from these mistakes, both customers and providers, and make our systems safer and more secure, that can be a good thing for the industry as a whole."
Network World staff writer Brandon Butler covers cloud computing and social media. He can be reached at BButler@nww.com and found on Twitter at @BButlerNWW.