Scaling Our Rate Limits to Prepare for a Billion Active Certificates

Let’s Encrypt protects a vast portion of the Web by providing TLS certificates to over 550 million websites—a figure that has grown by 42% in the last year alone. We currently issue over 340,000 certificates per hour. To manage this immense traffic and maintain responsiveness under high demand, our infrastructure relies on rate limiting. In 2015, we introduced our first rate limiting system, built on MariaDB. It evolved alongside our rapidly growing service but eventually revealed its limits: straining database servers, forcing long reset times on subscribers, and slowing down every request.