System Design Reliability

Why this module exists

Systems fail. Your job is to make failures predictable, contained, and recoverable. Reliability is not an afterthought — it is the design.

1) Observability

You can’t fix what you can’t see.

• Metrics: SLIs (latency, error rate, saturation)
• Logs: debugging and audit trails
• Traces: cross‑service latency breakdown

Signal: you can state your golden signals.

2) Failure Handling

Design for partial failure.

• Timeouts + retries with jitter
• Circuit breakers
• Bulkheads and load shedding

Signal: you can say what degrades first.

3) Idempotency & Deduplication

Retries are inevitable. Make them safe.

• Idempotency keys
• Exactly‑once is expensive; at‑least‑once is common

4) Security & Abuse Prevention

Threat modeling is scaling.

• Rate limits + quotas
• Authentication and authorization
• Data encryption in transit and at rest

Practice Prompts

1. Add circuit breakers to a checkout service.
2. Design rate limiting for a public API with bursts.
3. Decide what to drop first during overload.