CentOS 6
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Configure LVS (Linux Virtual Server)
2013/08/20
 
Configure LVS to build a load barancer.
This example shows to configure it on the environment below.
                          |
                          |
                      eth0|192.168.0.100
                    +----------+
--------------------|    LVS   |----------------------
                    +----------+
                      eth1|10.0.0.100
                          |
+----------+              |               +----------+
|          |10.0.0.30     |      10.0.0.31|          |
| Backend1 |------------------------------| Backend2 |
|   Web    | eth0                     eth0|    Web   |
+----------+                              +----------+

 
Packets to the eth0 on LVS Server are forwarded to Backend1 and Backend2 Servers with NAT.
Please change the default gateway to internal IP address of LVS on both Backend Web Servers first. (it's 10.0.0.100 on this example)
[1] Install ipvsadm
[root@gw ~]#
yum -y install ipvsadm
[root@gw ~]#
vi /etc/sysctl.conf
# line 7: change

net.ipv4.ip_forward =
1
[root@gw ~]#
sysctl -p
# reload

[root@gw ~]#
/etc/rc.d/init.d/ipvsadm start

ipvsadm: Clearing the current IPVS table: IPVS: Registered protocols (TCP, UDP, SCTP, AH, ESP)
IPVS: Connection hash table configured (size=4096, memory=64Kbytes)
IPVS: ipvs loaded.
[ OK ]
ipvsadm: Applying IPVS configuration: IPVS: [wlc] scheduler registered.
[ OK ]
[root@gw ~]#
chkconfig ipvsadm on

[2] Set ipvsadm
# clear tables first

[root@gw ~]#
ipvsadm -C
# add virtual service

# [ipvsadm -A -t (Service IP:Port) -s (Distribution method)]

[root@gw ~]#
ipvsadm -A -t 192.168.0.100:80 -s wlc

# add real servers

# [ipvsadm -a -t (Service IP:Port) -r (Real Server's IP:Port) -m] ("m" means masquerading (NAT))

[root@gw ~]#
ipvsadm -a -t 192.168.0.100:80 -r 10.0.0.30:80 -m

[root@gw ~]#
ipvsadm -a -t 192.168.0.100:80 -r 10.0.0.31:80 -m

# confirm tables

[root@gw ~]#
ipvsadm -l

IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  192.168.0.100:http wlc
  -> 10.0.0.30:http               Masq    1      0          0
  -> 10.0.0.31:http               Masq    1      0          0
# save the config

[root@gw ~]#
/etc/rc.d/init.d/ipvsadm save

ipvsadm: Saving IPVS table to /etc/sysconfig/ipvsadm: [ OK ]
[3]
It's OK all. Access to the Service IP address and make sure it works normally.
By the way, there are some Distribution method like follows.
Method Description
rr
Round Robin: distributes jobs equally amongst the available real servers.
wrr
Weighted 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.
lc
Least-Connection: assigns more jobs to real servers with fewer active jobs.
wlc
Weighted Least-Connection: assigns more jobs to servers with fewer jobs and relative to the real servers' weight (Ci/Wi). This is the default.
lblc
Locality-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.
lblcr
Locality-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.
dh
Destination Hashing: assigns jobs to servers through looking up a statically assigned hash table by their destination IP addresses.
sh
Source Hashing: assigns jobs to servers through looking up a statically assigned hash table by their source IP addresses.
sed
Shortest 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.
nq
Never 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.
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