您如何设计能够优雅地处理故障的系统？

Question

您如何设计能够优雅地处理故障的系统？

Accepted Answer

在大规模环境下，**故障是不可避免的** — 服务器崩溃、网络中断、依赖项变得不可用。为故障而设计意味着构建**能够容忍并从故障中优雅地恢复**的系统，而不是假设一切都正常工作。这对于可靠系统至关重要。

## 为故障而设计（心态）

```text
ASSUME things WILL fail → at scale, failures are NORMAL, not exceptional:
  → servers crash, networks partition, disks fail, dependencies go down, traffic spikes
  → design systems to EXPECT and HANDLE failures gracefully (not assume everything works)
→ "everything fails all the time" → build resilience in.
```

## 韧性技术

```text
✓ REDUNDANCY → multiple instances, no single point of failure (failover to healthy ones)
✓ RETRIES (with backoff) → retry transient failures (with exponential backoff + jitter to
  avoid overwhelming a recovering service)
✓ TIMEOUTS → don't wait forever for a failing dependency (fail fast)
✓ CIRCUIT BREAKERS → stop calling a failing service temporarily (prevent cascading failures;
  give it time to recover) → fail fast and fall back
✓ GRACEFUL DEGRADATION → reduced functionality vs total failure (e.g. show cached/partial
  data if a service is down)
✓ FALLBACKS → a default/alternative when something fails
✓ BULKHEADS / isolation → contain failures (one part failing doesn't sink everything)
```

## 避免级联故障

```text
⚠️ CASCADING failures → one failure triggers others (e.g. a slow service exhausts callers'
  resources → they fail too → spreads)
→ prevent with: timeouts, circuit breakers, isolation/bulkheads, load shedding, backpressure
✓ MONITORING/alerting → detect failures fast; test failure scenarios (chaos engineering)
```

## 为什么这很重要

理解如何设计能够优雅地处理故障的系统很重要，因为**在大规模环境下故障是不可避免的**，而为故障而设计对于可靠系统至关重要，因此这是重要的系统设计知识。

基本心态 — **假设事情会失败**（因为在大规模环境下，故障是常见的而不是例外 — 服务器崩溃、网络分区、依赖项宕机）以及设计系统来预期和优雅地处理故障而不是假设一切都能工作 — 是构建可靠系统的基础，体现在