N+1 capacity

Size every tier so that it still carries the peak after losing its largest unit, whether an instance, a zone or a whole region. Two regions each sized for half of the traffic are not redundant: when one fails, the other collapses under twice its load.

Where it shows up in real systems

  • Auto-scaling group

    Instances are added when CPU exceeds the target and removed when it falls. New instances need a warm-up period before taking traffic, so sudden spikes still hurt: keep enough minimum capacity. Failed instances are replaced automatically.

    In production: AWS Auto Scaling groups, Azure VM Scale Sets, GCP Managed Instance Groups, Kubernetes HPA

  • 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

See it break, then fix it

Build an architecture, send it a day of traffic and outages, and learn why it holds or fails. Free to start.

Open the learning path Open the sandbox