Why metrics? Since I joined 7digital I've seen the API grow from a brand new feature side by side with the (then abundant) websites to be the main focus of the company. The traffic grew and grew and keeps on growing in an accelerated pace and that brings us new challenges. We've brought the agile perspective into play which has made us adapt faster and make fewer errors but:

  • We can do unit tests but they don't bring out the behaviour.
  • We can do integration tests but they won't show the whole flow.
  • We can do smoke tests but they won't show us realistic usage.
  • We can do load test but they won't have realistic weighting.

Even when we do acceptance criteria we are actually being driven by assumptions, even with an experienced developer he is really just sampling all his previous work and as we move to a larger number of servers and applications it's not humanly possible to take all variables into consideration. It is common to hear statements like 'keep an eye on the error log/server log/payments log when releasing this new feature' but when something breaks it's all about 'what was released/when was it released/is it a specific server?'. As the data grows it becomes harder to sample and deduce from it quickly enough to feedback without causing issues, especially when agile tends to implement intermediary solutions which might have different behaviours from the final solution that have not been studied. The truth is that nothing replaces real life data and statistics – including developers opinions – if it the issue is a black swan then we need to churn out usable information fast!

Taken from @gregyoung This has been seen before by other companies; for example, Flickr on their Counting and Timing blog post. See also Building Scalable Websites by Flickr's Cal Henderson. This advice has been followed by other companies like Etsy on their Measure Anything Measure Everything blog post or Shopify on their StatsD blog post. How to do it? Decided to start with a winning horse I picked up the tools used by these companies: StatsD is described as “a network daemon for aggregating statistics (counters and timers), rolling them up, then sending them to graphite”. Graphite is described as “a highly scalable real-time graphing system. As a user, you write an application that collects numeric time-series data that you are interested i[...]. The data can then be visualized through graphite's web interfaces.” The way to implement these is available in several tutorials and I used StatsD own example C# client to poll our own API request log for API users, endpoints used, caching and errors. In the future it would be ideal for the application to access StatsD itself instead of running a polling daemon. There are a lot of usable features on Graphite. The ones I've used so far include Moving Average which will smooth out spikes in the graphs making it easier to see behaviour trends in a short time range and Sort by Maxima. There are even tools to forecast future behaviour and growth using Holt Winters Forecasting Statistics and this is used by companies to understand future scalability and performance requirements based on data from previous weeks, months or years (seen in this Etsy presentation on Metrics) How it looks and some findings Right away I got some usable results. An API client had a bug in their implementation which meant they required a specific endpoint more often than they would use it – this data can help out with debugging and also prevent abuse.

Sampled and smoothed usage per endpoint per API user...

Another useful graph is error rates, which might be linked with abuse, deploying new features or other causes.

 Error chart smoothed with a few spikes but even those are on the 0.001 % rate

Here is some useful caching information per endpoint to know how to tune up TTLs or look for stampede behaviour.

Sampled and smoothed Cache Miss per Endpoint

Opinion After you start using live data to provide feedback for your work there is no going back. It is my opinion that analysis of short and long term live results of any type of work should be mandatory as we move out of an environment that is small enough to be maintained exclusively by a team's knowledge.

Agile Development
Tuesday, March 17, 2015 - 12:49

I wanted to start looking at alternatives to our current set of cucumber feature tests. At the moment on the web team we're using using FireWatir and Capybara. So I though I'd take at look at what was available in Node.js. Many people think it's strange that a .Net shop would use a something written for testing Ruby or even consider something that isn't from the .Net community. Personally I think it's a benefit to truly look at something form the outside in.  Should it matter what you're using to drive your end product or what language your using to test it? Not really. So what are the motivations for moving away from Ruby, Capybara and FireWatir? In a word 'flaky', we've had heaps of issues getting our feature tests, AATs and smoke tests reliable. When it comes to testing, consistency should be king. They should be as solid as your unit tests.  If they fail you want to know that for definite you've broken something, rather than thinking it's a problem with the webdriver. It is with this aim in mind that I started looking at the following. Cucumber.js is definitely in it's infancy, there's lots of stuff missing but there's enough there to get going. Zombie.js is a headless browser, it claims to be insanely fast, no complaints here.

Tuesday, March 17, 2015 - 12:44

After seeing some relative success in our Solr implementations xml response times by switching on Tomcats http gzip compression, I've been doing some comparisons between the other formats solr can return. We use Solrnet, an excellent open source .NET Solr client. At the moment, it only supports xml responses, but every request sends the "Accept-encoding:gzip" header as standard, so all you have to do is switch it on on your server and you've got some nicely compressed responses. There is talk of supporting javabin de-serialisation, but it's not there yet. I've decided to compare the following using curl with 1000 rows and 10000 rows in json, javabin, json/gzip compressed and javabin/gzip compressed.

Wednesday, March 11, 2015 - 12:27


Following changes to our Catalogue API, we are releasing a change to the Basket API to support premium quality formats.

This release adds a package element below basketItem in all basket responses. This is to support the sale of music in different audio formats.

An example response would now look like this:

Tuesday, February 3, 2015 - 03:08

Guest Blog by John Nye on His First Week at 7digital

I have recently started at 7digital and already there are a few things of note that may seem small, but highlight the differences in attitude 7digital take over other companies I have worked for. Below are a few thoughts from my first week at 7digital.

Day 1 - Meet the team

After an incredibly frustrating start, owing to a 4 hour delay on my train journey, I was introduced to everyone, given my security pass and directed to a new starter guide that had a series of tasks that needed to be completed. These tasks ranged from installing software to getting added to email groups to reading up on the 7digital handbooks. So I logged into my Ubuntu machine and started going through the list... wait... Ubuntu?

Thoughts from the day:

  • Incredibly welcoming bunch.
  • Locate an Ubuntu book!

Day 2 - Empowerment