Why Twilio Segment Moved From Microservices Back To A Monolith

Microservices is a service-oriented software architecture in which server-side applications are constructed by combining many single-purpose, low-footprint network services. The touted benefits are improved modularity, reduced testing burden, better functional composition, environmental isolation, and development team autonomy. The opposite is a Monolithic architecture, where a large amount of functionality lives in a single service which is tested, deployed, and scaled as a single unit.

Twilio Segment adopted this as a best practice early-on, which served us well in some cases, and, as you’ll soon learn, not so well in others.

In the early days of Twilio Segment, we reached a tipping point with a core piece of Twilio Segment’s product. It seemed as if we were falling from the microservices tree, hitting every branch on the way down. Instead of enabling us to move faster, the small team found themselves mired in exploding complexity. Essential benefits of this architecture became burdens. As our velocity plummeted, our defect rate exploded.

Eventually, the team found themselves unable to make headway, with 3 full-time engineers spending most of their time just keeping the system alive. Something had to change. This post is the story of how we took a step back and embraced an approach that aligned well with our product requirements and needs of the team.

Twilio Segment’s customer data infrastructure ingests hundreds of thousands of events per second and forwards them to partner APIs, what we refer to as server-side destinations. There are over one hundred types of these destinations, such as Google Analytics, Optimizely, or a custom webhook.

Years back, when the product initially launched, the architecture was simple. There was an API that ingested events and forwarded them to a distributed message queue. An event, in this case, is a JSON object generated by a web or mobile app containing information about users and their actions. A sample payload looks like the following:

As events were consumed from the queue, customer-managed settings were checked to decide which destinations should receive the event. The event was then sent to each destination’s API, one after another, which was useful because developers only need to send their event to a single endpoint, Twilio Segment’s API, instead of building potentially dozens of integrations. Twilio Segment handles making the request to every destination endpoint.

If one of the requests to a destination fai

Source: HackerNews