How do you manage load failures and retries?

Managing load failures and retries involves designing systems to handle transient errors gracefully while avoiding cascading failures. When a request to a service or resource fails due to temporary issues like network glitches, timeouts, or temporary server overload, retries can help recover without user impact. However, retries must be implemented carefully to prevent overwhelming systems or creating infinite loops. The key is to distinguish between transient errors (e.g., a momentary network hiccup) and persistent ones (e.g., invalid credentials), retrying only the former.

A common strategy is to use exponential backoff with jitter. This means increasing the delay between retries exponentially (e.g., 1s, 2s, 4s) while adding randomness to avoid synchronized retry storms. For example, a client encountering a “503 Service Unavailable” error might wait 1 second for the first retry, 2 seconds for the second, and so on, with a random offset of ±500ms. Tools like AWS SDKs and libraries like Polly (for .NET) implement this pattern out of the box. Additionally, setting a maximum retry limit (e.g., 3-5 attempts) prevents endless loops. For critical operations, pairing retries with idempotent requests—such as using unique transaction IDs—ensures repeated attempts don’t cause unintended side effects.

Monitoring and logging are essential to refine retry logic. Track metrics like retry rates, success rates after retries, and latency to identify problematic dependencies. For example, if 30% of database calls require retries, it may indicate resource contention or misconfigured timeouts. Logging retry attempts with context (e.g., error type, retry count) helps debug issues. Circuit breakers (e.g., via Hystrix or resilience4j) can temporarily halt retries for a failing service, allowing it to recover. For instance, a circuit breaker might trip after 5 failures in 10 seconds, blocking further requests for 30 seconds. Combining these techniques ensures resilience without compromising system stability.