Retrofitting Fanout into 13-Year-Old Notification Architecture
Patreon revamped its notification pipeline using a two-stage fanout system.
Patreon redesigned its notification pipeline after an asynchronous task for millions of recipients began timing out. The new system employs a two-stage fanout approach, distributing recipient filtering and notification generation across batches, followed by payload distribution to independent email, push, and in-app delivery tasks. This post discusses horizontal scaling, failure isolation, task prioritization, and the challenges of implementing a new architecture without overhauling downstream systems.