Stability and Reliability key when Nelly prepares for Black Friday

30-07-2018, a market leader in Scandinavian online-retail, is about to launch their Black Friday campaign. The stakes are high, but months of planning and quick, responsive actions make sure that the servers excel during Black Friday.

Nelly is the go-to site for fashion interested men and women between the ages of 18 and 35. Nelly is also the place where the IT-department can rest easy during the busiest hours of Black Friday. The relaxed atmosphere is the result of a year of planning, testing and preparing for the huge sale during Black Friday. It’s a great sales opportunity involving the entire company – and rightfully so. Even though Black Friday is a fairly new phenomenon in Europe, the turnover was 230 million EUROs in 2015. In order to keep energy levels up during this intense day, Nelly provides their employees with breakfast, lunch and even a disco!


High expectations require healthy margins

One of the biggest challenges as an online-retailer on a day like Black Friday is trying to predict how many visitors the site will attract and what the visitors’ shopping behavior will look like. There are two factors that in combination make predictions especially difficult. The first is the whole idea of Black Friday – it’s a new kind of sales event to both e-commerce businesses and their customers. The second factor is the company’s overall ability to create successful marketing campaigns.



Dedicated servers and security in focus

The amount of traffic on Black Friday causes huge strains on the servers, so all technical planning is focused on creating stability and reliability. Since Black Friday is the busiest shopping day of the year, it’s a great test for the upcoming Christmas shopping, as well as the sales season that follows closely afterwards.

The planning is mainly focused on creating stable operations with short response times and avoiding any and all disruptions. Another key area is to create protection against unwanted visitors. Having a WAF-solution (Web Application Firewall) set up prior to the start of Black Friday and the Christmas season was highly prioritized. Nelly wanted to be able to channel all their energy and machine power on the right customers, which is why they had such a massive security focus.



Preparation, preparation, preparation

Last year’s Black Friday required a few changes in order to secure site stability and to improve the platform. Nelly and Basefarm started preparations for Black Friday and Christmas as early as May. So, how did we prepare?

  • Load tests – simulations of the anticipated market activity and visitor behavior
  • Load balancing – the load tests identified the need to make some changes in the load balancing. The physical servers that were already in place were supported by a cluster of virtual servers, as well as more physical servers, during this period.
  • A temporary expansion of its web front environment through an increased number of memcache.
  • Improvements to the program code in order to optimize response times.
  • Intrusion tests to increase safety.
  • Implementation of WAF (Web Application Firewall).

When plans meet reality

Black Friday got off to a great start. launched new deals every hour, keeping the interest levels spiked. However, there were some operational disruptions in the morning. The cause of the problem was difficult to identify at first. They figured out that the memcache memory reached its limit, even though an expansion was put in place in October. “Even with the thorough load tests, it’s difficult to anticipate shopping behaviors. It also taught us that new deals every hour create extreme peaks in visitor numbers.” says Henrik Palmqvist, CTO at Nelly.

Basefarm quickly added two extra memcache servers. Within 40 minutes of detecting the issue, was stable again. To be on the safe side, two additional servers were added before lunch.

The situation was under control for the rest of day.


Learning by doing

“We kept a close watch on the technical platform, but my team and I had a relaxing evening with chips, Coke and Counterstrike”, Henrik says. “We’ve had a great partnership with Basefarm, whith continuous dialog about what needs to get done before our Black Friday event. Our shared vision and goals were always first priority. Basefarm delivered on all their promises.” Henrik continues, “They were incredibly quick to react when we needed additional memcache servers.”

Last year’s Black Friday has given Henrik and his team great insight into how their platforms and applications behave. “This sales event gives me new ideas about how we can improve through increased scalability – and we’re going to get even better,” Henrik states. “As for this year: we’re going to be so well prepared, we can all play Counterstrike again.”


About Black Friday

Black Friday is a relatively new phenomena in Sweden. It caught on in 2013, and in 2015 the total turnover for the retail industry was 2.3 billion SEK. Half of the consumers shop in physical stores, and the other half shop online, according to PostNord.



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