Capacity planning is the process of sizing systems, networks, and support services so they can handle expected demand without failing or slowing down. It means estimating peak traffic, adding headroom, and deciding when to scale infrastructure, cache, queue requests, or limit expensive operations. In practice, this covers login services, payment checks, download servers, APIs, and database workloads.
In cyber security, capacity planning matters because overload can look like an attack and an attack can look like overload. A spike from a product launch, a flash sale, or a bot-driven denial-of-service campaign can exhaust shared resources and disrupt real users. Good planning uses load testing, rate limiting, autoscaling, circuit breakers, and clear fallback paths to keep critical services available. It also helps defenders spot unusual traffic faster, because they know what normal peak demand should look like.