Retry Pattern
// Definition
An application-level strategy for automatically re-issuing a failed HTTP request or operation, using a backoff delay between attempts to avoid overwhelming a recovering service. A retry policy defines: maximum retry count, delay strategy (fixed, linear, or exponential backoff), optional jitter, per-attempt timeout, and total deadline. Retries must only be applied to idempotent operations — retrying a non-idempotent request (such as a payment) can cause duplicate actions.
// Related terms
Exponential Backoff
A retry delay strategy where each successive attempt waits twice as long as the previous one: delay = base × 2^(attempt−1). Attempt 1 waits base ms, attempt 2 waits 2×base, attempt 3 waits 4×base. Prevents thundering-herd problems by spreading out retry load on a recovering service. Often combined with jitter (a random offset within the delay range) to avoid synchronised retry storms from multiple clients.
Timeout
A maximum duration allowed for an operation to complete before it is considered failed. In API and network testing: connection timeout (time to establish the TCP connection), read timeout (time to receive the full response after connecting), and total deadline (aggregate across all retry attempts). A timed-out request differs from a failed request — the status code, error type, and retry behaviour differ and must each be tested explicitly.
Idempotency
A property of an operation where calling it once and calling it many times produce the same effect. Critical for safe retries — GET, PUT, and DELETE are idempotent in HTTP semantics; POST is not. Tests should verify duplicate requests don't double-charge, double-create, or double-send.
Resilience Testing
Testing that a system degrades gracefully and recovers correctly under adverse conditions: slow networks, service timeouts, partial failures, high load, and dependency outages. Covers retry and timeout verification, circuit-breaker triggering, failover, and recovery-after-crash scenarios. Broader than chaos engineering (which targets production-level fault injection) — resilience testing is conducted in controlled test environments.