We want ClassDojo to be a delightful product for teachers and parents everywhere, and we've found that email is an effective channel to showcase awesome features and to offer help if our users need it. These emails are known as lifecycle emails, and the central idea is to send the right content to the right user at the right time.

Up until last year, we had been using third party services for lifecycle communication, but we grew increasingly frustrated with the limitations they presented, and decided to build our own system. So far, we are really happy with its capabilities, performance, and reliability!

This will be a three part blog series covering how we do lifecycle emails at ClassDojo. We'll start with an overview of the system and its architecture, move on to our experience using Redshift for this system in Part II, and finally explain some unique advantages our system offers compared off-the-shelf third party solution in Part III.

Class Story is one of our core product features at ClassDojo. It allows teachers to post photos and videos that parents can view, like, and comment on, and teachers around the world use it to share cute, funny, or exciting moments from their classrooms. Since we’re approaching the end of the school year, we wanted to provide teachers with a something memorable and engaging to send home. But with a ton of new projects we’d like to ship before back-to-school in August, we also wanted something we could build quickly.

We settled on a photo collage of a classroom’s top posts throughout the year. We generated collages for all classrooms with at least 9 posts this year and surfaced them in-app for teachers to share with their parents. We hope parents, teachers, and students everywhere will enjoy seeing a year’s worth of memories!

Here’s an example of one of the collages, using posts from our internal Class Story:

In the process, we wrote a simple npm module, photo-collage, which generates photo collages. You can view it here, and see the source code here.