A rate limiter decides, per caller, how many requests the system will accept in a given time (or how many it will process at once) and rejects or delays the rest, usually with HTTP 429 and a Retry-After header.
A Fallback is the "plan B" your service runs when a dependency call fails or is rejected (timeout, open circuit, bulkhead full, 5xx).
Retry & Backoff means that when a call to another service or resource fails with a *transient* error (a network blip, a 503, a throttling response, a deadlock victim), the caller waits a short, growing, randomised...
The Bulkhead pattern splits a service's shared resources (threads, connections, memory, queue slots, CPU) into isolated compartments, so that when one dependency or one traffic flow becomes slow or overloaded, only...
A circuit breaker sits between your service and a dependency it calls (a fraud-scoring API, a payment gateway, another microservice).
