Active-active and active-passive

Active-passive keeps a standby region that takes over on failure: simpler, but the standby is idle and failover takes minutes. Active-active serves traffic from every region at once: better latency and instant failover, but write conflicts must be handled.

Where it shows up in real systems

  • Global load balancer

    A single anycast IP attracts users to the nearest point of presence, then traffic rides the provider backbone to the best region. Unlike DNS failover, switching regions does not wait for resolver caches to expire.

    In production: AWS Global Accelerator, Google Cloud global external LB, Azure Front Door, Cloudflare Load Balancing

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