Bare metal refers to physical computing hardware — servers — on which software runs directly, without an intervening virtualisation layer (hypervisor). Bare metal deployments contrast with virtualised environments where physical servers run multiple virtual machines, each sharing underlying hardware resources.
Bare metal vs. virtual machines
On a virtualised server, a hypervisor (VMware ESXi, KVM, Hyper-V) creates and manages virtual machines. Each VM has a virtual CPU, virtual RAM, and virtual storage — mapped to physical resources by the hypervisor. This enables flexible resource allocation and strong isolation between workloads, but introduces CPU overhead (typically 5–15%), memory overhead (the hypervisor itself consumes memory), and latency (additional layer of abstraction for I/O).
On bare metal, there is no hypervisor. The OS and applications have direct access to physical CPUs, RAM, and storage. Performance is maximally efficient, and there is no overhead from virtualisation. The tradeoff is density: bare metal typically runs one workload per server, while virtualisation enables many workloads on shared hardware.
When bare metal is the right choice
Bare metal is appropriate for: latency-sensitive applications (high-frequency trading, real-time fraud detection); GPU-intensive workloads (ML training, inference at scale) where virtualisation overhead is prohibitive; security-sensitive environments where hypervisor-layer vulnerabilities are an unacceptable risk; and high-throughput storage and networking workloads where I/O performance is critical.
Kubernetes can run on bare metal — and this is increasingly common in enterprise environments that want cloud-native orchestration without the performance cost of virtualisation. The challenge is that bare metal provisioning (adding or replacing servers) is a physical process, unlike the API-driven instance provisioning in a cloud environment. Platforms that abstract bare metal provisioning — automated BIOS configuration, OS installation, cluster joining — close this operational gap.