dynamic_limit_req_zone

The dynamic_limit_req_zone directive is an essential component of the ngx_dynamic_limit_req_module, utilized to dynamically manage IP request rates and protect against abuse. It establishes a shared memory area where the current state of request rates for designated keys is maintained, allowing NGINX to control the frequency of requests that a single client can make to the server.

This directive accepts several parameters:
- key: Specifies the key to track requests, which can be a combination of text and variables (e.g., $binary_remote_addr enables tracking based on the client IP address).
- zone=name:size: Defines the name and size of the shared memory zone; name is an identifier, and size defines the amount of memory allocated (e.g., 5m for 5 megabytes).
- rate=rate: Establishes the maximum request rate (in requests per second) allowed for the key, expressed as integers corresponding to 0.001 requests per second (e.g., 5r/m for five requests per minute).
- sync: Optional flag for enabling synchronization between processes.
- redis=address: Specifies the Redis server location for storing request states externally.
- block_second=time: Defines a time duration (in seconds) for which an IP should be blocked after exceeding the allowed rate.

Overall, dynamic_limit_req_zone helps mitigate issues like DDoS attacks by controlling the request flow and allowing for dynamic adjustments based on traffic patterns.