Fault Tolerance

ELI5 - The Vibe Check

Fault tolerance is designing a system that assumes parts of it will break, so it plans for that instead of hoping it doesn't happen. A fault-tolerant system doesn't just survive a server crashing, it barely notices, because it was built from the start with the expectation that servers crash.

Real Talk

Fault tolerance is the property of a system that allows it to continue functioning correctly, without interruption, even when one or more of its components fail. It differs subtly from resilience, which allows continuing in a degraded state, by aiming for continued correct operation despite faults, commonly implemented through redundancy, replication, error detection and correction, and automatic failover, and is a prerequisite for high availability.

Show Me The Code

async function fetchWithFallback(primary, backup) {
  try {
    return await primary()
  } catch (err) {
    console.warn('primary failed, falling back', err)
    return await backup()
  }
}

When You'll Hear This

"The cache node died but the cluster is fault tolerant, nobody even noticed." / "Fault tolerance means the system survives the failure, not just recovers from it eventually."