Your server is slow — and it's your neighbor's fault

In the cloud, your virtual machine rarely gets a physical server to itself. Instead, a hypervisor slices one beefy machine into many VMs belonging to different customers — this is multi-tenancy, and it's what makes cloud computing cheap. The catch: some resources can be cleanly partitioned, but others are shared and fought over.

CPU cores and RAM are usually reserved per tenant, so you get your slice. But disk I/O, network bandwidth, and even the CPU's shared cache are harder to fence off. When a co-located tenant suddenly runs a huge database export or a traffic spike, it saturates those shared channels — and your app slows down even though your own CPU and memory look nearly idle. This is the noisy neighbor problem.

The tell-tale sign is performance that tanks for no reason you can see in your own metrics. Cloud providers fight it with resource quotas, I/O throttling, and by spreading tenants across hardware. As a user, you can escape it by paying for dedicated instances (a whole physical host) or provisioned IOPS (guaranteed disk throughput) — trading some of the cloud's cost savings for predictable performance.