LWM-Linux/10 - Containers and Vitrualization/Kernel Virtualization (KVM).md

# Kernel-based Virtual Machine (KVM) virtualization

## 1. Introduction to KVM

KVM (Kernel-based Virtual Machine) is an open-source virtualization technology built into the Linux kernel. It allows the kernel to function as a hypervisor, enabling a host machine to run multiple isolated virtual environments called virtual machines (VMs) or guests.

## 2. Key Features of KVM

- Full virtualization: KVM provides hardware-assisted virtualization using Intel VT or AMD-V technologies.
- Scalability: Can support numerous guest VMs on a single host.
- Security: Uses SELinux and seccomp for enhanced security.
- Performance: Near-native performance for VMs.
- Linux integration: Seamlessly integrates with the Linux ecosystem.

## 3. KVM Architecture

KVM consists of three main components:

a) A kernel module (kvm.ko) that provides the core virtualization infrastructure.
b) A processor-specific module (kvm-intel.ko or kvm-amd.ko).
c) QEMU for hardware emulation.

## 4. Hardware Requirements

- 64-bit x86 processor with hardware virtualization support (Intel VT-x or AMD-V)
- Sufficient RAM and storage for host and guest systems
- BIOS/UEFI with virtualization support enabled

## 5. Installation

On most Linux distributions, you can install KVM using the package manager:

`sudo apt install qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils`

## 6. Creating and Managing VMs

You can create and manage VMs using command-line tools or graphical interfaces:

### a) Command-line tools:
- virsh: CLI for managing VMs
- virt-install: For creating new VMs

### b) Graphical tools:
- virt-manager: User-friendly GUI for VM management
- Cockpit: Web-based interface for system administration, including VM management

## 7. Networking

KVM supports various networking modes:

- NAT (Network Address Translation)
- Bridged networking
- Routed networking
- Isolated networking

## 8. Storage

KVM supports multiple storage options:

- Local disk storage
- Network-attached storage (NAS)
- Storage Area Networks (SAN)
- Distributed storage systems (e.g., Ceph)

## 9. Live Migration

KVM supports live migration, allowing you to move running VMs between physical hosts with minimal downtime.

## 10. Performance Tuning

To optimize KVM performance:

- Use virtio drivers for guest I/O
- Enable huge pages for memory management
- Use CPU pinning to dedicate physical cores to VMs
- Implement I/O throttling to prevent resource contention

## 11. Monitoring and Management

Tools for monitoring KVM environments:

- libvirt API
- virt-top
- Prometheus with node_exporter
- Grafana for visualization

## 12. Security Considerations

- Use SELinux or AppArmor for mandatory access control
- Implement network segmentation
- Regularly update and patch both host and guest systems
- Use secure protocols for remote management

## 13. Backup and Disaster Recovery

- Use snapshots for point-in-time backups
- Implement regular full VM backups
- Consider replication for critical VMs

## 14. Integration with Cloud Platforms

KVM is the foundation for many cloud platforms:

- OpenStack
- oVirt
- Proxmox VE

## 15. Comparison with Other Virtualization Technologies

KVM vs:
- VMware vSphere: KVM is open-source and often more cost-effective
- Xen: KVM is integrated into the Linux kernel, potentially offering better performance
- Hyper-V: KVM provides better Linux guest support

## 16. Best Practices

- Regularly test and validate backups
- Implement proper capacity planning
- Use automation tools for provisioning and management
- Keep documentation up-to-date

## 17. Troubleshooting

Common issues and solutions:
- Performance problems: Check resource allocation and use monitoring tools
- Boot failures: Verify VM configuration and hardware compatibility
- Network issues: Check network configuration and firewall settings