Rate Limiting at the Application Layer

Rate limiting at the application layer is crucial for preventing resource abuse and ensuring system reliability, especially in scenarios involving costly workloads like those of large language models (LLMs). This approach is favorable for freemium or non-revenue-correlated apps to prevent a single user from generating excessive requests. The article discusses implementing rate limiting using two primary models: the token bucket, which allows for a continuous flow of tokens and can handle bursts of traffic, and the fixed window, which issues tokens at set intervals. Both methods can be efficiently managed using a database with strong ACID guarantees, ensuring transactional evaluations and fairness through token reservation. While application-layer rate limiting effectively manages most traffic loads, it can falter under extreme conditions like DDoS attacks. The article further explores techniques such as the use of jitter to prevent thundering herds, reservation of tokens for fairness and efficiency, and strategies for authenticating anonymous users. It emphasizes the importance of a reliable backend platform like Convex, which offers transactional guarantees and fast database access to support these implementations.