Editing Rate limiting (section)

== Protocol servers ==

Protocol servers using a request / response model, such as [[FTP server]]s or typically [[Web server]]s may use a central [[In-memory database|in-memory]] [[key-value database]], like [[Redis]] or [[Aerospike (database)|Aerospike]], for session management. A rate limiting algorithm is used to check if the user session (or IP address) has to be limited based on the information in the session cache. 

In case a client made too many requests within a given time frame, [[Hypertext Transfer Protocol|HTTP]] servers can respond with status code [[List of HTTP status codes#429|429: Too Many Requests]].

However, in some cases (i.e. web servers) the session management and rate limiting algorithm should be built into the application (used for dynamic content) running on the web server, rather than the web server itself.

When a protocol server or a network device notice that the configured request limit is reached, then it will offload new requests and not respond to them. Sometimes they may be added to a [[Queue (data structure)|queue]] to be processed once the input rate reaches an acceptable level, but at peak times the request rate can even exceed the capacities of such queues and requests have to be thrown away.