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Linux Virtual Server

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Original author(s)Wensong Zhang
Developer(s)et al.
Initial releaseMay 1998; 27 years ago (1998-05)
Written inC
Operating systemLinux
Typeload balancing
LicenseGNU General Public License
Websitewww.linuxvirtualserver.org

Linux Virtual Server (LVS) is load balancing software for Linux operating systems.

LVS is a free and open-source project started by Wensong Zhang in May 1998, subject to the requirements of the GNU General Public License (GPL), version 2. 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.

Overview

The major work of the LVS project is now to develop advanced IP load balancing software (IPVS), application-level load balancing software (KTCPVS), and cluster management components.

  • IPVS: an advanced IP load balancing software implemented inside the Linux kernel. The IP Virtual Server 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.

LVS can be used for building highly scalable and highly available network services, such as web, email, media and VoIP services, and integrating scalable network services into large-scale reliable e-commerce or e-government applications. LVS-based solutions already have been deployed in many real applications throughout the world, including Wikipedia.

The LVS components depend upon the Linux Netfilter framework, and its source code is available in the net/netfilter/ipvs/ subdirectory within the Linux kernel source. LVS 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.

Schedulers

LVS implements several balancing schedulers, listed below with the relevant source files:[1]

  • 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)

Userland

The userland utility program used to configure LVS is ipvsadm(8). It can be executed by the superuser only.

Glossary

  • 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[2]

IP addresses

  • 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[2]

Examples

Setting up a virtual HTTP server with two real servers: 

ipvsadm -A -t 192.168.0.1:80 -s rr
ipvsadm -a -t 192.168.0.1:80 -r 172.16.0.1:80 -m
ipvsadm -a -t 192.168.0.1:80 -r 172.16.0.2:80 -m

The first command assigns TCP port 80 on IP address 192.168.0.1 to the virtual server. The chosen scheduling algorithm for load balancing is round-robin (-s rr). The second and third commands are adding IP addresses of real servers to the LVS setup. The forwarded network packets shall be masked (-m).

Querying the status of the above configured LVS setup: 

# ipvsadm -L -n
IP Virtual Server version 1.0.8 (size=65536)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  192.168.0.1:80 rr
  -> 172.16.0.2:80                Masq    1      3          1
  -> 172.16.0.1:80                Masq    1      4          0

References

  1. ^ "Job Scheduling Algorithms in Linux Virtual Server". linuxvirtualserver.org. 2011-02-08. Retrieved 2013-11-24.
  2. ^ a b http://bobcares.com/blog/?p=184


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