At what stage of development or level of qualification should a request rate limiting mechanism be implemented?

The rate limiting mechanism should be implemented at the system architecture design stage, especially if high load or external API interactions are expected.

In terms of qualification level — this is a task for middle and above, as it requires understanding of network protocols, application architecture, and potential attacks (e.g., DoS).

Implementing rate limiting helps protect the service from overloads, ensures fair resource distribution, and improves stability.

Example: in Go, token bucket or leaky bucket algorithms can be used to limit the number of requests per second.