Nov 25, 20214 min read

Behind the scenes on Black Friday.


by Klarna

Martin Elwin, Engineering Director and Domain Lead of the Purchase Experience domain.

Right at the center of the Black Friday shopping frenzy, you’ll find Klarna. In 2020 Klarna processed over 5 million transactions during Friday alone – and this year, we’re anticipating even higher volumes. How do we prep our solutions prior to the event and what’s happening behind the scenes during our merchants’ flash sale events? We met with Martin Elwin, Engineering Director and Domain Lead of the Purchase Experience domain, to understand how Klarna ramps up for the yearly peak season.

Hey Martin. Tell us what are you up to the days before Black Friday begins?
I’m leading the Purchase Experience domain, which is where we handle most integrations with merchants. We are the entry point into the Klarna ecosystem for many of our products and solutions like Klarna Payments, Klarna Checkout, On-Site Messaging, and In-Store solutions. During Black Friday and shopping peak season, all these solutions handle a lot of traffic, so we have to make sure that our products are ready. 

How do you estimate the purchase volumes, and how are you prepping to make sure we can satisfy this demand?
First, we use information about previous traffic and predicted growth together with input from merchants performing flash sales. This helps us estimate what we need to handle for each solution during the peak period. On top of the estimated load, we add a multiplying factor to ensure we have a safety margin in terms of capacity. The challenge is that different parts of our systems have diverse requirements and optimization possibilities. Our teams spend a lot of time identifying these and tuning the systems to perform better. In addition to the testing and tuning, we prepare how to handle different scenarios that could happen on this day.

What makes Black Week different from any other week? 

As a part of our Black Friday preparation, we have a “freeze” period when all the peak season preparations must be completed.  It’s a safety measure to avoid making last-minute changes during our busiest time of the year, and it’s very intense up until that point. 

The fact that we can not make any more changes is a bit different, and everyone is on the edge of their seats looking at how everything is going. We know that some merchants put a lot of their workload on us during specific flash sale events, and these events tend to be quite exciting. We work hard to make sure that we can handle such events without issues. It’s thrilling to see if all the preparations we’ve done are successful.

Millions of transactions. What could go wrong? 

Last year, we processed nearly 5,5 million transactions during Black Friday, and we had over 10, 000 transactions during our busiest minute of the day. Despite these great numbers, last year’s Black Friday wasn’t overly exciting for us – which is totally fine. My idea of a successful Black Friday is to be in bed sleeping when we are done. I don’t want any surprises that keep us up and working through the night. 

Every year, Black Friday gets more challenging and complex, as we have more teams and systems involved. The worst-case scenario is obviously that we fail to live up to the expectations of our customers – the consumers, merchants, and partners. The worst, WORST, case is that we are completely down and nothing is working. 

How do you identify potential issues?

During Black Friday, we gather remotely and in the offices to monitor our systems carefully. We want people at hand to act quickly if something happens. Most times, it has been calm and kinda nice – just chatting with colleagues, eating some pizza, and seeing the numbers ticking up on the dashboards. Hopefully, we’ll have a calm evening and a great night of sleep this year!