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Twitter’s Story: How Homegrown Load Testing Tools Can Misfire

If Twitter built their own tool to perform their own load test, why did the selfie cause their site to crash?

The selfie that changed the world, or at least Twitter, has been in the news for the past month. On March 2, 2014, the infamous Oscar selfie of Ellen and her celebrity friends broke a record of 2 million retweets before midnight the same night. That record was previously set by President Barack Obama, hugging first lady Michelle Obama after his 2012 re-election.

The selfie caused Twitter to crash for more than 20 minutes, also breaking the record for the longest crash of the social media site. Twitter was infamous for crashing in its early days (anyone remember "Fail Whale?"), so it's no wonder the social media giant worked extra hard to completely prepare their website infrastructure before going public in November 2013. This included building their own load testing tool, Iago, in 2012.

If they built their own tool to perform their own load test, why did the selfie cause their site to crash? The Oscar selfie crash is a perfect example of what companies can easily overlook. Twitter did not test their users properly and their homegrown tool clearly doesn't solve all of their problems... their servers still crash.

What is Iago and why did Twitter decide to make it? And what does that have to do with your decision to use homegrown tools versus vendor load testing tools? Don't worry, we will tell you.

Twitter's Homegrown Load Testing Tool: Iago
Iago was created in June of 2012 by Twitter's internal engineering team. According to Twitter, Iago is a load generator created to help the social media site test services before they encounter production traffic. Chris Aniszczyk, Head of Open Source at Twitter, said, "There are many load generators available in the open source and commercial software worlds, but Iago provided us with capabilities that are uniquely suited for Twitter's environment and the precise degree to which we need to test our services."

Basically their homegrown tool was completely customized for their platform alone - a very attractive aspect of developing your own tool.

The three attributes Twitter focused on in creating Iago were:

  1. High performance: Iago was designed to generate traffic in a precise and predictable way, to minimize variance between test runs and allow comparisons to be made between development iterations.
  2. Multi-protocol: Modeling a system as complex as Twitter can be difficult, but it's made easier by decomposing it into component services. Once decomposed, each piece can be tested in isolation; which requires the load generator to speak each service's protocol. Twitter has in excess of 100 such services, and Iago tests most of them using built-in support for the internal protocols Twitter uses.
  3. Extensible: Iago is designed for engineers. It assumes the person building the system will also be interested in validating performance. As such, the tool is designed from the ground up to be extensible - making it easy to generate new traffic types, over new protocols and with individualized traffic sources.

Why Twitter Couldn't Handle Ellen's Selfie
If we were to do the math, Iago was up and running for nearly two years before the Oscar selfie. What happened to their load testing tool?

There were two main reasons why Twitter crashed. First, the tweet Ellen posted was a picture. On Twitter, a tweet accounts for only 260 bytes of data while a picture on Twitter accounts for 33KB of data, almost 130 times as much as a tweet. Second, Twitter's distributed server system was already at max capacity so the load taken on by the website couldn't be distributed to any nearby servers.

Twitter made one major mistake contributing to the crash back in March: they didn't anticipate and replicate real user activity. Most likely Iago wasn't instructed to generate a load based on a picture being retweeted millions of times, thus Twitter didn't know what to expect when the Oscars rolled around.

Homegrown Tool vs. Vendor Load Testing Solutions
Twitter was looking for a DIY homegrown solution because of their unique platform, and while most load testing tools seek to accomplish the same goal, there are always differences between tools. Here are some of the differences we see between homegrown and vendor-provided load testing tools.



1. You can customize it - A homegrown tool, created completely from scratch, means you can build exactly what you think you need. But you don't get the benefit of lots of other people's experiences - so what you think you need may not turn out to be what you actually need.

2. Homegrown tools are free like a puppy is free - We have mentioned this analogy before in another post, and it needs to be brought up again. Homegrown tools aren't really free. You have to pay a team to keep them up and running.

3. What if someone leaves? - A couple of developers are experts on the tool they built, but what happens when they leave? Who is going to be your expert? If the new person isn't properly trained and if the code isn't well documented, then modifications to the code become extremely difficult.

1. Your vendor makes it extensible - A vendor that supports lots of users is constantly adding features and capabilities to support needs you may not have realized you have yet. With extensible APIs and SDKs, you still have the ability to add integrations and the protocol support your application demands.

2. You pay for something that works - With homegrown tools there is no guarantee that it will work 100% of the time. By paying a vendor to use their tool, you have assurances that your load testing tool won't let you down when you need it most.

3. Support Team - Vendors dedicate people to work on any issues and keep you worry-free. Their team of experts is available to make sure all of your questions and concerns are addressed.

Homegrown Tools Are Not for Everyone
Twitter's tool has done well to help them improve the performance of the service, but continued service disruptions show that it isn't perfect. A homegrown tool isn't always the best solution, and most of the time, companies do not have the resources handy to completely build their load testing tool from scratch. If you are interested in learning more about vendor options, give us a call. We're more than happy to help.

More Stories By Tim Hinds

Tim Hinds is the Product Marketing Manager for NeoLoad at Neotys. He has a background in Agile software development, Scrum, Kanban, Continuous Integration, Continuous Delivery, and Continuous Testing practices.

Previously, Tim was Product Marketing Manager at AccuRev, a company acquired by Micro Focus, where he worked with software configuration management, issue tracking, Agile project management, continuous integration, workflow automation, and distributed version control systems.

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