Linux Virtual Server is an advanced load balancing

Load balancing (computing)

Load balancing is a computer networking methodology to distribute workload across multiple computers or a computer cluster, network links, central processing units, disk drives, or other resources, to achieve optimal resource utilization, maximize throughput, minimize response time, and avoid...

 solution for Linux

Linux

Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...

 systems. It is an open source

Open source

The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...

 project started by Wensong Zhang in May 1998. The mission of the project is to build a high-performance and highly available server for Linux using clustering technology, which provides good scalability, reliability and serviceability.

Purpose and Function

The major work of the LVS project is now to develop advanced IP load balancing

Load balancing (computing)

Load balancing is a computer networking methodology to distribute workload across multiple computers or a computer cluster, network links, central processing units, disk drives, or other resources, to achieve optimal resource utilization, maximize throughput, minimize response time, and avoid...

 software (IPVS), application-level load balancing software (KTCPVS), and cluster management components.

• IPVS
  IP Virtual Server
  IPVS implements transport-layer load balancing inside the Linux kernel, so called Layer-4 LAN switching. IPVS is incorporated into Linux Virtual Server, where it runs on a host and acts as a load balancer at the front of a cluster of real servers, it can direct requests for TCP/UDP based services...
  
  : is an advanced IP load balancing software implemented inside the Linux kernel
  Linux kernel
  The Linux kernel is an operating system kernel used by the Linux family of Unix-like operating systems. It is one of the most prominent examples of free and open source software....
  
  . The IP Virtual Server
  IP Virtual Server
  IPVS implements transport-layer load balancing inside the Linux kernel, so called Layer-4 LAN switching. IPVS is incorporated into Linux Virtual Server, where it runs on a host and acts as a load balancer at the front of a cluster of real servers, it can direct requests for TCP/UDP based services...
  
   code was already included into the standard Linux kernel 2.4 and 2.6.
• KTCPVS: implements application-level load balancing inside the Linux kernel, currently under development.

Users can use the LVS solutions to build highly scalable and highly available

High-availability cluster

High-availability clusters are groups of computers that support server applications that can be reliably utilized with a minimum of down-time. They operate by harnessing redundant computers in groups or clusters that provide continued service when system components fail...

 network services, such as web, email, media services and VoIP services, and integrate scalable network services into large-scale reliable e-commerce or e-government applications.

The LVS solutions have already been deployed in many real applications throughout the world, including Wikipedia.

The LVS component depends upon the Linux Netfilter framework and its source code is available in the net/netfilter/ipvs/ subdirectory within the kernel source. It implements several balancing schedulers, listed below with the relevant source file:

• Round-Robin (ip_vs_rr.c)
• Weighted Round-Robin (ip_vs_wrr.c)
• Least-Connection (ip_vs_lc.c)
• Weighted Least-Connection (ip_vs_wlc.c)
• Locality-Based Least-Connection (ip_vs_lblc.c)
• Locality-Based Least-Connection with Replication (ip_vs_lblcr.c)
• Destination Hashing (ip_vs_dh.c)
• Source Hashing (ip_vs_sh.c)
• Shortest Expected Delay (ip_vs_sed.c)
• Never Queue (ip_vs_nq.c)

List retrieved from http://www.linuxvirtualserver.org/docs/scheduling.html

The module is able to handle UDP, TCP layer-4 protocols as well as FTP passive connection by inspecting layer-7 packets. It provides a hierarchy of counters in the /proc/ directory.

The userland tool is ipvsadm.

Major Terms

• LVS DIRECTOR or simply Director: The load balancer that receives all incoming client requests for services and directs them to a specific "real server" to handle the request.

• REAL SERVERS: The nodes that make up an LVS cluster which are used to provide services on the behalf of the cluster.

• CLIENT COMPUTERS: The computers requesting services from the Virtual Server.

Section Reference

IP address Names

• VIP - Virtual IP address: The IP address used by the Director to provide services to client computers.

• RIP - Real IP address: The IP address used to connect to the cluster nodes.

• DIP - Directors IP address: The IP address used by the Director to connect to network of Real IP addresses.

• CIP - Client IP address: The IP address assigned to a client computer, that it uses as the source IP address for requests being sent to the cluster.

Section Reference

External links

• The Linux Virtual Server project
• Linux Virtual Server Configuration Wiki