backend-resilience-patterns

Backend Resilience Patterns

Purpose

Protect backend services from cascading failures by applying circuit breakers, retries with backoff, bulkheads, timeouts, and fallbacks. Resilience is not optional — every external call must be wrapped in fault-tolerance patterns.

Agent Protocol

Trigger

Exact user phrases: "resilience", "circuit breaker", "retry", "bulkhead", "timeout", "fallback", "resilience4j", "fault tolerance", "retry strategy", "backoff", "rate limiter".

Input Context

• Type of external calls (HTTP, database, message queue).
• Existing retry or timeout configuration.
• SLAs and latency requirements.

Output Artifact

Configuration snippets or code. No file unless requested.

Response Format

Pattern: {circuit-breaker|retry|bulkhead|timeout|fallback}
Config: {key parameters and values}

Completion Criteria

• At least timeout configured for every external call.
• Retry with exponential backoff and jitter configured.
• Circuit breaker defined per dependency (not one for all).
• Fallback handler defined for every circuit breaker.
• Bulkhead isolation applied to thread pools where needed.

Max Response Length

4 lines per pattern. 20 lines for full configuration.

Architecture Decision Tree

Which Resilience Pattern?

What type of failure are you protecting against?
  ├── Slow responses (server busy, GC pause, overloaded)
  │   └── Timeout + Circuit Breaker
  ├── Transient failures (network blip, connection reset, DNS failure)
  │   └── Retry with backoff + Circuit Breaker
  ├── Resource exhaustion (thread pool, connection pool, memory)
  │   └── Bulkhead + Circuit Breaker
  ├── Downstream service completely down
  │   └── Circuit Breaker + Fallback
  └── Client sending too many requests
      └── Rate Limiter + Bulkhead

Pattern Composition Order

How should patterns be composed?
  ┌─────────────────────────────────┐
  │ 1. Timeout (outermost)          │  ← Fail fast
  │ 2. Bulkhead (semaphore limit)   │  ← Isolate resources
  │ 3. Circuit Breaker              │  ← Stop cascading failures
  │ 4. Retry (innermost)            │  ← Retry transient failures
  │ 5. Fallback (catch-all)         │  ← Degrade gracefully
  └─────────────────────────────────┘