Scaling the Nylas Cloud data layer became crucial following the unexpected surge in users after the launch of their open-source email app, Nylas N1, in October 2015. Initially supported by a simple architecture using Amazon RDS for MySQL, the rapid influx of users highlighted significant bottlenecks and led to a major outage. To address these challenges, Nylas implemented a series of technical upgrades, including moving from RDS to self-managed MySQL on EC2, utilizing ProxySQL for efficient query management, and horizontally sharding their data to distribute load. This transition allowed Nylas to handle the increased data demands with near-zero downtime, leveraging a flexible and resilient architecture. The process involved creating a new mechanism for mapping object IDs to their respective shards, ensuring high availability with automated failover systems, and dynamically routing queries to optimize performance. These changes were implemented swiftly within three weeks, demonstrating the team's focus on scalability and reliability, setting the stage for further enhancements to their application layer.