Domino's Pizza UK CIO Colin Rees says people should be wary of swallowing the notion that the cloud is infinitely scalable.
"There's this myth that you move something to the cloud and you have this infinitely scalable environment" — Colin Rees
Discussing the pizza delivery firm's shift to the cloud, Rees told a Cloud Expo audience in London that certain challenges are frequently discussed: security, control, data location and support.
But, according to Rees, the one not mentioned is capacity planning. "There's this myth that you move something to the cloud and you have this infinitely scalable environment. It's kind of true but that [scalability] comes at a price and needs to be managed carefully," he said.
Domino's has experienced a period of rapid expansion in the UK, opening 60 new stores per year. From just over 20 percent in 2008, now more than 50 percent of its delivered sales come from the web and, of that, 20 percent from mobile transactions.
He said planning IT resources is essential for dealing with that high growth and the high demand on the franchised operation's e-commerce infrastructure.
Demand created by the online operation has big peaks, typically between 5pm and 9pm and on Tuesdays, Fridays and Saturdays — Tuesdays because of the Two for Tuesday promotion. However the peaks created by corporate apps and the online business do not coincide.
"The opportunity for us for moving to the cloud is twofold: one is I want to be able to buy IT services to satisfy those peaks so I'm not buying IT infrastructure to deal with that highest load. The second is about flexibility," Rees said.
He cited the recent period before Christmas as an example of why he needs to plan to exploit that flexibility. "It was rainy, it was horrible, it was cold. People like a takeaway in those circumstances. But the weather wasn't so bad that we couldn't get our drivers out to deliver. It was the perfect weather for pizza sales," Rees said.
"We had a capacity plan that showed we were going to run out of capacity. That night we upped the number of processors in our servers and the following day we were able to validate that that had had the desired effect. And that sort of agility is where we see some of the big benefits of being in the cloud."
E-commerce platform and corporate systems
Domino's operates two datacentres: a primary site running the e-commerce platform and corporate systems, and a secondary site for web backup and development and testing.
"Our e-commerce platform is all virtual but it's not currently a cloud service. In the back-up site we're running all our development and test servers in the cloud," he said.
"We're taking the approach of learning and building our knowledge and experience of operating in that environment. Throughout this year we'll start testing and trialling, and moving our e-commerce platform over to cloud services."
But Rees said it's not scaling at any cost. "By having a model of how you expect your capacity to increase, you can compare your actual performance against that model, which helps you understand inefficiencies caused by the application," he said.
"Now, if you don't do that, you have no baseline against which to measure your applications, and therefore, yes, you may well scale infinitely but you may find you costs go up as well at the same rate.
"So our challenge is to make sure our developers are kept honest and always building the most efficient application because that will always be the cheapest to run."
Finite capacity behind cloud services
Danny Quilton, performance management specialist at Capacitas, which advises Domino's on capacity planning, said people talk about the cloud as if it were an abstract entity. "But really there are physical servers behind it — there's finite capacity behind cloud services," he said. "There's no magic there."
He added that he recently spoke to a large enterprise that was experiencing issues with the scalability of a cloud service.
"Scaling up a handful of instances was no problem at all but when you ask them to scale at short notice an additional 200 instances, there was a very large lag from requesting that to delivery. That's where the market is at the moment, but it may mature beyond that," Quilton said.