🔸 TL;DR
Resilient APIs don’t “just work” — they fail gracefully.
Timeouts, retries, rate limiting, throttling, idempotency keys, circuit breakers and bulkheads are your toolkit to survive latency spikes, dependency failures and traffic storms ⛈️
🔸 WHAT IS API RESILIENCE?
Designing APIs so that when things go wrong (and they will), your system:
▪️ Degrades gracefully
▪️ Protects itself and its dependencies
▪️ Avoids cascading failures
▪️ Keeps a good UX instead of hanging forever
🔸 KEY PATTERNS TO KNOW
🔹 Timeouts ⏱️
▪️ Never wait forever on a downstream service
▪️ Define reasonable timeouts per call (external APIs, DB, message broker…)
▪️ Better a controlled failure than a hanging request
🔹 Retry Mechanism 🔁
▪️ Retry only for transient errors (network glitch, 502, 503…)
▪️ Use backoff (exponential) and a max retry count
▪️ Combine with idempotency to avoid duplicate side effects
🔹 Rate Limiting 🚦
▪️ Limit how many requests a client can send per time window
▪️ Protects your API from abuse and sudden spikes
▪️ Often implemented as “429 Too Many Requests” with headers
🔹 Throttling 🧯
▪️ Similar to rate limiting but from the provider perspective
▪️ Smooths traffic by slowing down or queuing requests
▪️ Protects internal resources from overload
🔹 Idempotency Key 🔑
▪️ Same request + same key 👉 same effect, even if sent multiple times
▪️ Critical for payment, order creation, emails, etc.
▪️ Avoids double charges and duplicated resources when clients retry
🔹 Circuit Breaker ⚡
▪️ When a dependency keeps failing, “open” the circuit and stop calling it
▪️ Return a fallback or an error immediately instead of waiting
▪️ Prevents cascading failures and protects your upstream services
🔹 Bulkhead 🧱
▪️ Isolate resources by pool (per client, per feature, per dependency)
▪️ If one area is overloaded, it doesn’t sink the whole system
▪️ Think: separate thread pools / connection pools / queues
🔸 TAKEAWAYS 💡
▪️ Resilience is a design choice, not a framework checkbox
▪️ Combine patterns: timeout + retry + idempotency + circuit breaker is a classic combo
▪️ Always think in terms of failure scenarios and blast radius
▪️ The goal is not “never fail”, but “fail in a controlled, user-friendly way”
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