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Virtualization & Containers

Virtualization allows multiple operating systems to run concurrently on a single physical machine by abstracting the hardware.

Types of Virtualization​

Full Virtualization​

The Guest OS is unaware that it's running in a virtual machine. The Hypervisor intercepts and emulates all privileged instructions.

  • Example: VMware, VirtualBox.

Para-virtualization​

The Guest OS is modified to be aware that it's running in a virtual environment. It makes special system calls (hypercalls) to the Hypervisor instead of attempting to execute privileged instructions directly.

  • Example: Xen (early versions).

The Hypervisor (VMM)​

The Virtual Machine Monitor (VMM), or Hypervisor, is the software that manages and isolates virtual machines (VMs).

  • Type 1 (Bare Metal): Runs directly on the hardware (e.g., Xen, VMware ESXi).
  • Type 2 (Hosted): Runs as an application on top of a host OS (e.g., KVM, VirtualBox).

Containers​

Containers provide a lighter-weight form of isolation by sharing the host's kernel while isolating the user space.

Key Linux Technologies for Containers​

  • Namespaces: Provide process isolation (e.g., PID, Network, Mount). Each container has its own view of the system.
  • Cgroups (Control Groups): Limit and monitor resource usage (e.g., CPU, Memory, Disk I/O).
  • Union File System (UnionFS): Allows combining multiple directories into a single file system view (e.g., OverlayFS).
FeatureVirtual Machine (VM)Container
IsolationHardware-level (Strong)Process-level (Moderate)
Guest OSFull OS per VMShared host kernel
Startup TimeMinutesSeconds
Resource UsageHigh (full OS overhead)Low (shared resources)

Docker and Orchestration​

  • Docker: The most popular platform for building, shipping, and running containerized applications.
  • Kubernetes (K8s): An orchestration platform for managing large-scale container deployments across a cluster of machines.