Behind the scenes @ Coolblue HQ

What is Coolblue?

Last week I was invited to go visit Coolblue behind the scenes in Rotterdam, NL. Coolblue has always been one of my favorite online dutch/belgian webshops because of their great customer service, their clear but simple websites, and most important, their great range of products at very affordable prices.

They roughly have about 50k unique products in 150-200 different webshops (they launch 2 new webshops per week on average), which they all have in stock at all time in one of their huge warehouses. Their biggest warehouse is more than 40.000 square meters which is about 10-20 FIFA football fields! How big is that! Ordering before 23.59 means it’s delivered at your doorstep for free the next day, or the same day when paying additional shipping costs. Also on sunday!

Why would they organise behind the scenes events?

The main idea behind this ‘Behind the scenes’ is that they are looking for talent programmers. They’re looking for roughly 100 new developers. They have about 40 right now so it seems they have big plans. Are they going international? Who knows! But their CEO didn’t really deny it. Their global employee basis is about 750 people.

Since I’m a freelancer I won’t be able to work for them so why did I go to this event? Well.. because their main dev talk was about scalability. I find this a very interesting and challenging topic so getting insights from one of the biggest webshops in the Benelux was a great opportunity for me to learn.

So what did I learn at Coolblue?

  1. use microservices / hypermedia api’s to flatten out your infrastructure. This allows you to easily isolate bugs and/or maintain those API’s without having to retest stable services on every deploy.
  2. every microservice uses an isolated datastore. CouchDB for customer data, PostgreSQL for order+payment information, ElasticSearch for the product catalog.
  3. RabbitMQ as a central state change notification mechanism. This is the glue between your microservices.
  4. use git pull requests to review & validate your team members changes
  5. CentOS RPM packages to distribute everything
  6. Puppet labs or Chef to install & maintain your (virtual) servers
  7. Statsd + Graphite for advanced reporting
  8. Nagios for alerting
  9. Create a “Chaos Monkey”. It’s single purpose is to once in a while kill your live environment. Your devs should then come with solutions to auto-fix these downtimes. This is how Netflix stayed online during the massive AWS outage a while ago:

Have a look at the slides from their software architect.

Why should you attend one of these meetings?

  1. If you want a developer job @ Coolblue obviously.
  2. If you want to learn more about scalability.
  3. If you want to network with hundreds of other devs.

Inform yourself on this page:

Here’s a nice dutch article about the same event:

A/B split testing with PHP

What is split testing?

A/B split testing is the art of setting up multiple random variants/tests in a controlled experiment. Example tests are different call to actions, different types/locations of buttons, different images, etc.
Your goal? Finding the best converting test, learn from this, and implement this further in your website, thus getting more & more conversions out of existing visitors. Learn why people click and don’t click.


Why should you use split testing?

When using split testing, you’ll learn how your visitors think, what works best on your site, and how you can get the most out of all visitors. Optimising websites takes time, but this time may be cheaper then putting another 1000$ in advertising. First optimise, then do some more advertising.

How can you split test in PHP?

There are several PHP libraries which you can use for split testing, and I tested most of them. Here’s my favourites:

Must we use PHP libraries?

Nope.. There are several other ways to integrate split testing in your projects. Here’s some more:

What should we test? Example tests:

And here’s some more articles to help you get started..


Any feedback or tips & tricks regarding split testing are more than welcome in the comment section. Good luck!

Google Universal Analytics: the next big thing?

Today I came across a video about Universal Analytics, Google’s self-proclaimed next big thing.

But is it really? In short? Yes! Here’s why.

What is the difference between Google Analytics and Google Universal Analytics?

Universal Analytics tracks much more than just visits to a website likes Google Analytics does. Where Google Analytics (based on Urchin) tracks visits, Universal Analytics tracks visitors. This allows us to do cross-device tracking which mean even more detailed statistics!


Offline conversions

With the Measurement Protocol you’re now able to ‘plug in’ extra user data, provided by offline/external appliances such as an RFID chip, apps, sensors, etc. Have a look at the YouTube video in my introduction. As a geek, I absolutely love this. The more data the merrier.

Customisable session timeouts

You can now alter this ourselves. Previously this limit was a hard fixed 30 minutes.


Ga.js becomes analytics.js. The include code also changes.

universal analytics code

Custom dimensions/metrics

Custom dimensions/metrics allows you to create specific metrics in combination with your CRM’s database. See this as custom variables 2.0.

External cost structure

External input, external output. We’re now able to import external costs structures so we can calculate our conversions and ROI even more accurate. Back in the old days.. we could only import Google Adwords costs.

And much, much more..

Here’s some more useful and interesting links I found about Google Universal Analytics:

Did I forgot to mention something very important about Universal Analytics? Please leave a note in the comments 🙂