Rate limiting in asp.net core

 There are 4 rate limiting algorithms:

• Fixed window
• Sliding window
• Token bucket
• Concurrency

Fixed window : The AddFixedWindowLimiter method uses a fixed time window to limit requests. When the time window expires, a new time window starts and the request limit is reset.

below are steps to configure fixed window rate limiter

1. Add Rate Limiter:

       builder.Services.AddRateLimiter(_ => _

                .AddFixedWindowLimiter(policyName: fixedPolicy, options =>

                {

                    options.PermitLimit = myOptions.PermitLimit;//2, getting values from config

                    options.Window = TimeSpan.FromSeconds(myOptions.Window);//2000 

                    options.QueueProcessingOrder = QueueProcessingOrder.OldestFirst;

                    options.QueueLimit = myOptions.QueueLimit;// 2

                    

                }      

             ));

2.      app.UseRateLimiter();

3. call RequireRateLimiting("policyname like fixed") either on minimal api endpoint or MapControllerwithDefaultRoute().

4. We can use [EnableRateLimiter] , [DisableRateLimiter] attributes if we don't want to configure rate limiter globally.

5 we can configure multiple ratelimiting policies on AddRateLimiter and we can use specific policy for specific controller/Action method.

concurrency limiter :

The concurrency limiter limits the number of concurrent requests. Each request reduces the concurrency limit by one. When a request completes, the limit is increased by one. Unlike the other requests limiters that limit the total number of requests for a specified period, the concurrency limiter limits only the number of concurrent requests and doesn't cap the number of requests in a time period