Virtual Machines (VMs) are software-based emulations of physical computers. They allow multiple operating systems (OSes) to run on a single physical server or host machine simultaneously. Each VM operates independently, as if it were a separate physical computer, with its own OS and applications. Here are key aspects of virtual machines:
- Hypervisor: VMs are managed and orchestrated by a hypervisor, a software or hardware component that creates and manages virtualized environments. Hypervisors include Type 1 (bare-metal) and Type 2 (hosted) hypervisors.
- Isolation: VMs are isolated from each other and the host system. This means that issues in one VM, such as a crash or security breach, typically do not affect other VMs or the host.
- Guest OS: Each VM runs its own guest OS, which can be different from the host OS. This allows for the coexistence of various OSes on the same physical hardware.
- Resource Allocation: VMs can be allocated specific amounts of CPU, memory (RAM), storage, and network resources. Resource allocation can be adjusted dynamically to meet workload requirements.
- Snapshots: VMs often support the creation of snapshots, which are point-in-time images of the VM’s state. Snapshots can be used for backup, recovery, and testing purposes.
- Templates: VM templates, also known as images, allow for the rapid deployment of standardized VM configurations. Templates are a time-saving feature in virtualization.
- Live Migration: Some hypervisors support live migration, allowing VMs to be moved from one physical host to another without downtime, ensuring high availability.
- Cloning: VMs can be cloned to create identical copies. This is useful for scaling applications or creating development and testing environments.
- Resource Overcommitment: Hypervisors often support resource overcommitment, where more VMs are provisioned than there are physical resources. This is done based on the assumption that not all VMs will use their allocated resources simultaneously.
- Virtual Networking: VMs can be connected to virtual networks that are isolated from physical networks. Network configurations, including IP addresses and routing, can be managed at the virtual level.
- Security: VMs can be segmented and secured using virtual firewalls and security policies. Isolation between VMs enhances security by limiting the impact of security breaches.
- Application Testing: VMs are commonly used for application development, testing, and staging, providing a sandboxed environment for software development.
- Legacy System Support: VMs can run older or legacy OSes and applications, helping organizations maintain compatibility with older software.
- Cost Savings: By consolidating multiple VMs on a single physical server, organizations can reduce hardware costs, data center space, and power consumption.
Popular hypervisors for creating and managing virtual machines include VMware vSphere/ESXi, Microsoft Hyper-V, KVM (Kernel-based Virtual Machine), and Xen. These technologies are foundational to server virtualization, cloud computing, and data center optimization. VMs have become integral to modern IT infrastructure, offering flexibility, scalability, and resource efficiency.