Backpressure communicates that a downstream component is overloaded so upstream work can slow, wait or be rejected in a controlled way. It prevents an ever-growing queue from consuming resources while latency and failure rates worsen.
A suitable policy defines bounded queues, request priorities and understandable rejection or retry behavior. Adding processing capacity can help, but a system still needs a way to handle bursts and failed dependencies without allowing unlimited work to accumulate.
ELI5
Backpressure is a system saying it cannot take more work at the current pace. It slows the incoming flow or turns away some requests so the work already accepted can finish.
For example, if an AI service can handle only a limited number of simultaneous requests, it may ask new callers to wait or return a clear busy response instead of allowing its queue to grow without limit.
Why reject work instead of accepting everything?
Unlimited queues can exhaust resources and make every request unreliable. Controlled rejection can preserve service for accepted work.
Does more capacity make backpressure unnecessary?
No. Sudden bursts or downstream failures can overwhelm even a larger system, so bounded overload handling remains useful.
