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