SCALING OUR RATE LIMITS TO PREPARE FOR A BILLION ACTIVE CERTIFICATES

Summary from the TLDR Web Dev newsletter

Let's Encrypt, a free certificate authority, faced challenges scaling its rate-limiting system to handle over 550 million websites and 340,000 certificate requests per hour. Its initial MariaDB-based system wasn't enough, as it caused slowdowns and frustrated users with long wait times. To address this, the company migrated to a Redis-based system that used the Generic Cell Rate Algorithm (GCRA), allowing it to handle a billion active certificates and even addressing the issue of "zombie clients" making repeated failed requests.