Editing Linux Virtual Server

{{Short description|Load-balancing software}}
{{Infobox software
| name                   = Linux Virtual Server
| title                  = 
| logo                   = Lvslogo.png
| logo caption           = LVS official logo
| logo_size              = 200px
| logo_alt               = LVS official logo
| screenshot             = <!-- Image name is enough -->
| caption                = 
| screenshot_size        = 
| screenshot_alt         = 
| collapsible            = 
| author                 = Wensong Zhang
| developer              = et al.
| released               = {{Start date and age|1998|05}}
| discontinued           = 
| latest release version = 
| latest release date    = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} -->
| latest preview version = 
| latest preview date    = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} -->
| programming language   = [[C (programming language)|C]]
| operating system       = [[Linux]]
| platform               = 
| size                   = 
| genre                  = [[Load balancing (computing)|load balancing]]
| license                = [[GNU General Public License]]
| website                = {{URL|http://www.LinuxVirtualServer.org}}
}}

'''Linux Virtual Server''' ('''LVS''') is [[Load balancing (computing)|load balancing]] software for [[Linux kernel]]&ndash;based 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 [[Computer cluster|clustering]] technology, which provides good scalability, reliability and serviceability.

== Overview ==
[[File:Wikipedia webrequest 2022.png|thumb|LVS as used by [[Wikimedia Foundation]] in 2022.]]

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

* [[IP Virtual Server|IPVS]]: an advanced IP load balancing software implemented inside the [[Linux kernel]]. The [[IP Virtual Server]] code is merged into versions 2.4.x and newer of the Linux kernel mainline.<ref>{{cite web
 | url = http://www.linuxvirtualserver.org/software/ipvs.html
 | title = IPVS Software - Advanced Layer-4 Switching
 | date = 2011-02-08 | accessdate = 2014-01-12
 | publisher = linuxvirtualserver.org
}}</ref>
* KTCPVS: implements application-level load balancing inside the Linux kernel, {{As of|2011|02|lc=yes}} still under development.<ref>{{cite web|author=Wensong Zhang |url=http://www.linuxvirtualserver.org/software/ktcpvs/ktcpvs.html |title=KTCPVS Software - Application-Level Load Balancing |publisher=Linuxvirtualserver.org |date=2011-02-08 |accessdate=2014-03-25}}</ref>

LVS can be used for building highly scalable and [[High-availability cluster|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 <code>net/netfilter/ipvs</code> 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 <code>/proc</code> directory.

The [[userland (computing)|userland]] utility program used to configure LVS is called [[ipvsadm]], which requires [[superuser]] privileges to run.

=== Schedulers ===
LVS implements several balancing schedulers, listed below with the relevant source files:<ref>{{cite web
 | url = http://www.linuxvirtualserver.org/docs/scheduling.html
 | title = Job Scheduling Algorithms in Linux Virtual Server
 | date = 2011-02-08 | accessdate = 2013-11-24
 | publisher = linuxvirtualserver.org
}}</ref>

* Round-robin (<code>ip_vs_rr.c</code>)
* Weighted round-robin (<code>ip_vs_wrr.c</code>)
* Least-connection (<code>ip_vs_lc.c</code>)
* Weighted least-connection (<code>ip_vs_wlc.c</code>)
* Locality-based least-connection (<code>ip_vs_lblc.c</code>)
* Locality-based least-connection with replication (<code>ip_vs_lblcr.c</code>)
* Destination hashing (<code>ip_vs_dh.c</code>)
* Source hashing (<code>ip_vs_sh.c</code>)
* Shortest expected delay (<code>ip_vs_sed.c</code>)
* Never queue (<code>ip_vs_nq.c</code>)
* Maglev hashing (<code>ip_vs_mh.c</code>)

== Glossary ==
Commonly used terms include the following:<ref name="Bob">{{cite web
 | url = http://bobcares.com/blog/linux-virtual-server-load-balance-your-networked-services/
 | title = Linux Virtual Server: Load Balance Your Networked Services
 | year = 2008 | accessdate = 2013-11-24
 | publisher = bobcares.com
}}</ref>
* ''LVS director'': load balancer that receives all incoming client requests for services and directs them to a specific "real server" to handle the request
* ''Real servers'': nodes that make up an LVS cluster which are used to provide services on the behalf of the cluster
* ''Client computers'': computers requesting services from the virtual server
* ''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

== Examples ==
Setting up a virtual [[Hypertext Transfer Protocol|HTTP]] server with two real servers:

<syntaxhighlight lang="bash">
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
</syntaxhighlight>

The first command assigns [[Transmission Control Protocol|TCP]] port 80 on [[IP address]] [[private network|192.168.0.1]] to the virtual server.  The chosen scheduling algorithm for [[Load balancing (computing)|load balancing]] is [[Round-robin scheduling|round-robin]] (<code>-s rr</code>).  The second and third commands are adding IP addresses of real servers to the LVS setup.  The forwarded network packets shall be masked (<code>-m</code>).<ref>{{cite news |last1=Peter |first1=Jeff |title=Understanding Virtual Server |url=https://xaro.net/blog/understanding-vps-vs-vds-guide/ |access-date=18 June 2023}}</ref>

Querying the status of the above configured LVS setup:

<syntaxhighlight lang="text">
# 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
</syntaxhighlight>

== See also ==
{{Portal|Linux|Free and open-source software}}
* [[IP Virtual Server]]
* [[Netfilter]] and [[nftables]]
* [[Network scheduler]]

== References ==
{{reflist}}

==External links==
* {{Official website|http://www.LinuxVirtualServer.org/}}
* [http://kb.linuxvirtualserver.org/wiki/Main_Page Linux Virtual Server Configuration Wiki]
* [http://publib-b.boulder.ibm.com/Redbooks.nsf/9445fa5b416f6e32852569ae006bb65f/e8417f0abc3cadaf85256d40004f31b8?OpenDocument&Highlight=0,SG247034 IBM eServer BladeCenter, Linux, and Open Source: Blueprint for e-business on demand] {{Webarchive|url=https://web.archive.org/web/20220811174534/https://publib-b.boulder.ibm.com/Redbooks.nsf/9445fa5b416f6e32852569ae006bb65f/e8417f0abc3cadaf85256d40004f31b8?OpenDocument&Highlight=0,SG247034 |date=2022-08-11 }} (includes LVS as a component)

{{Linux kernel}}

[[Category:High-availability cluster computing]]
[[Category:Free network-related software]]
[[Category:Internet software for Linux]]
[[Category:Linux-only free software]]
[[Category:Parallel computing]]