What's the biggest problem when you try to reach 97% of the UK adult population with a Christmas ad campaign?
According to Marks and Spencer, it's the possibility your website might crash under the sheer number of people visiting to vote on the name of a dog.
Its multi-million pound 2013 Christmas ad campaign, called Magic & Sparkle, encouraged TV viewers to visit its microsite to help name a Scottie found in the ad by Rosie Huntington-Whiteley (as well as buy things, of course).
To cope with the predicted traffic, the high street retailer created the site on Microsoft Azure, as well as save on the costs of physical servers and internal IT resources had it created the site in-house.
It also plumped for developing in the cloud because of the time savings: in Azure it took a week, compared to an estimated two months in-house.
"We had no idea exactly when these interactions would take place, so the whole site design had to be elastic and able to scale to cope with the potentially huge volumes of traffic," says John Pillar, the chain store's head of software engineering for mobile, labs, retail IT and digital stores.
"M&S is a brand that relies on trust and if the additional traffic had slowed the e-commerce site and made it hard for consumers to purchase products, that would have been unacceptable."
He opted to go to the cloud for the project when execs first came to him with the ad proposal in October last year.
Aside from a cute dog, the advert featured a host of celebrities including Huntington-Whiteley and Helena Bonham-Carter, and the last thing the high street retailer wanted was its microsite to freeze when people tried to visit it.
Having worked with staff from Azure before to create "e-stores" in Amsterdam, Pillar and his team decided to go with the Redmond business again to take advantage of its on-demand compute, storage, content delivery, and networking capabilities.
"We had a matter of weeks to get the Magic & Sparkle website up and running, and knew that Microsoft Azure would provide us with the speed, scale, and elasticity that such an important campaign required," says Pillar.
"By using Azure, we could have the site up in hours if needed. If we engaged with our internal infrastructure team, it would take days just to build the server, so in terms of work hours, using Azure is invaluable."
However, when a demo site was tested, the volume of traffic M&S was predicting for the real thing created a bottleneck.
The Microsoft Services Premier Support team responded by dedicating a section of its Amsterdam data centre to the project, and supplied testing software too.
"Testing was critical," says Pillar. "We quickly engaged with Microsoft Services through the Premier Support for Developers programme, where the team helped us make sure that the technology could scale at the levels we required."
While M&S refrained from noting how many website visitors they had over the holiday season, Pillars says the proof is in the (Christmas) pudding.
"The biggest endorsement of Azure is that we have used it again for campaigns of a similar nature - for Valentine's Day, Mother's Day and many more holidays," says Pillar. "We know that if a campaign goes viral and the traffic goes crazy, Azure will scale to whatever levels we need.
"Using Azure for short-term projects is extremely affordable. In terms of team productivity, Azure provides a massive boost for M&S."