Rate limiter algorithms

 ASP.NET Core supports rate limiting middleware that can be used to limit the number of requests that a web API can handle based on different criteria. Some of the rate limiting algorithms that can be used in ASP.NET Core are1 :

• Fixed window: This algorithm uses a fixed time window to limit requests. When the time window expires, a new time window starts and the request limit is reset. This algorithm is simple and easy to implement, but it can create spikes of traffic at the beginning or end of each window.
• Sliding window: This algorithm uses a rolling time window to limit requests. It keeps track of the timestamps of each request and rejects any incoming request that exceeds the limit within the current window. This algorithm is more accurate and fair than fixed window, but it requires more memory and computation.
• Token bucket: This algorithm assigns tokens to each client and replenishes them at a constant rate. Each request consumes one token from the client’s bucket. If the bucket is empty, the request is rejected or queued until a token is available. This algorithm allows for some bursts of traffic and gives clients more flexibility.
• Concurrency: This algorithm limits the number of concurrent requests that a client can make. It uses a semaphore to control the access to the resource. If the semaphore is full, any incoming request is rejected or queued until a slot is available. This algorithm ensures that the resource is not overloaded by too many simultaneous requests.

To use rate limiting in ASP.NET Core, you need to reference the System.Threading.RateLimiting NuGet package and configure the rate limiting policies and options in your Startup class. You also need to create a custom DelegatingHandler subclass that implements the rate limiting logic and attaches it to your HttpClient or HttpMessageHandler. You can also use attributes like EnableRateLimiting and DisableRateLimiting to control which endpoints require rate limiting or not.