This article is shared from Tianyi Cloud Developer CommunityWhat is the difference between libvirt and qga?》, author: Le Dao
Libvirt is an open source project that provides a set of APIs, tools, and libraries for managing and controlling virtualization platforms.
In Openstack environment, Libvirt is a crucial component that provides a unified interface for various virtualization technologies such as KVM, QUME, Xen and LXC, so that Openstack can interact with the underlying virtualization technologies.
Libvirt's main functions include:
1. API provides: Libvirt provides a C language API, and also supports binding of multiple high-level programming languages. These APIs allow developers to write applications to create, configure, and manage virtual machines
2. Virtualization management interface: Libvirt provides a unified interface that can transparently handle different virtualization technologies. This means that Openstack does not need to know the specific virtualization implementation, but operates through libvirt, simplifying development and maintenance work
3. Security isolation: Libvirt supports security policies to ensure isolation between each virtual machine and improve system security
4. Resource Management: Libvirt can control and adjust the resource allocation of virtual machines, including CPU, memory, disk and network. This is crucial for optimizing resource utilization in virtualized environments
5. Network management: Libvirt provides a network abstraction layer, which can create and configure network bridges, network filters, etc., and supports the management of virtual network devices.
6. Storage management: Libvirt supports multiple storage types, such as block devices, file systems, network storage, and Cinder storage services in Openstack.
In Openstack, Libvirt mainly interacts with the following services:
1. nova: As an Openstack computing service, nova performs these operations by calling Libvirt's API, including creating, starting, stopping and migrating virtual machine instances.
2.neutron: Openstack network service neutron can use Libvirt to configure virtual networks, such as setting network connections, port security rules and load balancing.
3. cinder: cinder directly interacts with the back-end storage system, but Libvirt participates in the mount and unmount of volumes, as well as the cinder volume used inside the virtual machine.
Libvirt also includes some command line tools, such as virsh, etc., which allow administrators to directly operate on virtual machines, such as viewing status, editing configuration, mounting disks, etc.
Libvirt is a key component in the Openstack architecture. It serves as an intermediate layer to connect upper services and underlying virtualization technology, providing efficient, flexible and secure virtualization management capabilities.
Understanding and mastering the working principles and functions of Libvirt is very important for Openstack operations and developers.
QGA (Qemu Guest Agent, qemu-guest-agent) and Libvirt are two components that play different roles in virtualized environments, and there are significant differences between them.
QGA（Qemu Guest Agent）
1. Definition and function:
QGA is a normal application running inside a virtual machine (the executable file name is qemu-ga by default, and the service name is qemu-guest-agent by default).
Its main purpose is to implement a network-dependent interaction method between the host and the virtual machine, but rather it depends on virtio-serial (the default preferred method) or isa-serial.
QGA interacts with the socket channel on the host through read and write serial port devices. The interaction protocol is the same as QMP (QEMU Monitor Protocol), that is, data exchange is used in JSON format.
2. Functional features:
QGA provides query and modification capabilities for internal state information of virtual machines (such as file system information, network information, etc.).
It can perform some host-initiated operations, such as file operations, disk management, network configuration, etc.
QGA's function extension is relatively convenient, and developers can add new commands or functions by modifying the source code.
The difference between QGA and Libvirt
Position and role:
QGA runs inside the virtual machine and serves as a communication bridge between the virtual machine and the host.
Libvirt runs on the host and serves as a unified management and operation platform for virtualization technology.
Functional range:
QGA is mainly responsible for querying and modifying the internal state information of the virtual machine, as well as performing the operations initiated by the host.
Libvirt provides comprehensive virtual machine management functions, including life cycle management, resource allocation, remote management, etc.
Interaction method:
QGA interacts with the socket channel on the host through the serial port device and uses JSON format for data exchange.
Libvirt interacts with virtualization technology on the host through its API libraries, daemon and command line tools.
Scalability:
QGA's function extension is relatively easy, and developers can add new commands or functions by modifying the source code.
The scalability of Libvirt is mainly reflected in its support for a variety of virtualization technologies and a unified API interface.
To sum up, QGA and Libvirt play different roles in virtualized environments, with their own unique functions and characteristics. They work together to provide strong support and guarantee for the application of virtualization technology.