Backpressure

When a component cannot keep up, it signals upstream to slow down instead of silently queueing forever. Bounded queues, 429 responses and pull-based consumers are all forms of backpressure.

Where it shows up in real systems

  • Rate limiter

    Protects the system from abusive clients and retry storms by answering HTTP 429 above the limit. Fixed windows let bursts through at window edges; sliding windows and token buckets are smoother.

    In production: Envoy rate limit service, Redis + Lua, NGINX limit_req, Cloudflare Rate Limiting

  • Message queue

    A queue absorbs spikes: the API answers as soon as the message is stored, and workers drain the backlog at their own pace. Standard queues deliver at least once and may reorder; FIFO queues keep order but cap throughput. Messages that fail repeatedly go to a dead-letter queue.

    In production: Amazon SQS, RabbitMQ, Azure Service Bus, Google Cloud Tasks

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