Configure LVS (Linux Virtual Server) to build a load arancer.

This example is based on the environment below.

--------------------|    LVS   |----------------------
----- ---- 
------------             |              ------------ 
|  Backend01 |   ||  Backend02 |
| Web Server  ------------ -------------  Web Server |
|            |eth0                  eth0|            |
------------                            ------------

HTTP packets to the eth0 on LVS Server are forwarded to Backend01 and backend02

Servers with NAT

Change the default gateway to internal IP address of LVS on both Backend Web Servers first.(It’s on the example)

[1]Install ipvsadm

[[email protected] ~]# yum -y install ipvsadm
# enable IP forward
[[email protected] ~]# echo 'net.ipv4.ip_forward = 1' >> /etc/sysctl.conf 
[[email protected] ~]# sysctl -p
[[email protected] ~]# touch /etc/sysconfig/ipvsadm 
[[email protected] ~]# systemctl start ipvsadm 
[[email protected] ~]# systemctl enable ipvsadm 

[2] Configure Load Balancing.

# clear tables
[[email protected] ~]# ipvsadm -C
# add virtual service
# [ ipvsadm -A -t (Service IP:Port) -s (Distribution method) ]
[[email protected] ~]# ipvsadm -A -t -s wlc 
# add backend real servers
# [ ipvsadm -a -t (Service IP:Port) -r (Real Server's IP:Port) -m ] ("m" means masquerading (NAT))
[[email protected] ~]# ipvsadm -a -t -r -m 
[[email protected] ~]# ipvsadm -a -t -r -m 
# confirm tables
[[email protected] ~]# ipvsadm -l 
IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
-> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP wlc
->               Masq    1      0          0
->               Masq    1      0          0

[3]It’s OK,Access to the Service IP address and make sure it works normally.

By the way,there are some Distribution method like follows,


rrRobin Robin
distributes jobs equally amongst the available real servers.
wrrWeighted Round Robin
assigns jobs to real servers propor-tionally to there real servers weight. Servers with higher weights receive new jobs first and get more jobs than servers with lower weights. Servers with equal weights get an equal dis-tribution of new jobs.
assigns more jobs to real servers with fewer active jobs.
wlcWeighted Least-Connection
assigns more jobs to servers with fewer jobs and relative to the real servers’ weight (Ci/Wi). This is the default.
lblcLocality-Based Least-Connection
assigns jobs destined for the same IP address to the same server if the server is not overloaded and available, otherwise assign jobs to servers with fewer jobs, and keep it for future assignment.
lblcrLocality-Based Least-Connection with Replication
assigns jobs destined for the same IP address to the least-con- nection node in the server set for the IP address. If all the node in the server set are over loaded, it picks up a node with fewer jobs in the cluster and adds it in the sever set for the target. If the server set has not been modified for the speci-fied time, the most loaded node is removed from the server set, in order to avoid high degree of replication.
dhDestination Hashing
assigns jobs to servers through looking up a statically assigned hash table by their destination IP addresses.
shSource Hashing
assigns jobs to servers through looking up a statically assigned hash table by their source IP addresses.
sedShortest Expected Delay
assigns an incoming job to the server with the shortest expected delay. The expected delay that the job will experience is (Ci 1) / Ui if sent to the ith server, in which Ci is the number of jobs on the the ith server and Ui is the fixed service rate (weight) of the ith server.
nqNever Queue
assigns an incoming job to an idle server if there is, instead of waiting for a fast one, if all the servers are busy, it adopts the Shortest Expected Delay policy to assign the job.