VM vs Container — Kernel-sharing vs Hypervisor

Two ways to isolate a workload

Both VMs and containers solve the same problem: run multiple workloads on one machine without them stepping on each other. They take fundamentally different approaches.

Virtual Machines — full OS per instance

A hypervisor (VMware ESXi, KVM, VirtualBox, Hyper-V) sits between hardware and guest VMs. Each VM runs a complete operating system: its own kernel, its own init system, its own userland. Isolation is hardware-enforced — VMs can't see each other's memory or syscalls.

Containers — shared kernel, isolated namespaces

A container shares the host's kernel. Isolation is achieved with Linux namespaces (separate views of PIDs, network, mounts, hostnames, IPC, user IDs) and cgroups (CPU/memory/IO limits). No guest OS. No hypervisor. Just a bundle of processes that think they are alone on a machine.

The trade-off table

Most application workloads — web services, databases, batch jobs — fit comfortably inside container isolation. Use VMs when you need different kernels, hard isolation between tenants, or a Windows guest on Linux.