Configure LVS (Linux Virtual Server)2015/06/10

Configure LVS (Linux Virtual Server) to build a load barancer.
This example is based on the environment below.

                          |
                          |
                      eth0|192.168.0.30
                    +----------+
--------------------|    LVS   |----------------------
                    +-----+----+
                      eth1|10.0.0.30
                          |
+------------+            |             +------------+
|  Backend01 |10.0.0.51   |    10.0.0.52|  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 10.0.0.30 on the example)
[1]	Install ipvsadm.

[root@dlp ~]#

yum -y install ipvsadm

# enable IP forward

[root@dlp ~]#

echo 'net.ipv4.ip_forward = 1' >> /etc/sysctl.conf

[root@dlp ~]#

sysctl -p

[root@dlp ~]#

touch /etc/sysconfig/ipvsadm

[root@dlp ~]#

systemctl start ipvsadm

[root@dlp ~]#

systemctl enable ipvsadm

[2]	Configure Load Balancing.

# clear tables

[root@dlp ~]#

ipvsadm -C

# add virtual service

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

[root@dlp ~]#

ipvsadm -A -t 192.168.0.30:80 -s wlc

# add backend real servers

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

[root@dlp ~]#

ipvsadm -a -t 192.168.0.30:80 -r 10.0.0.51:80 -m

[root@dlp ~]#

ipvsadm -a -t 192.168.0.30:80 -r 10.0.0.52:80 -m

# confirm tables

[root@dlp ~]#

ipvsadm -l

IP Virtual Server version 1.2.1 (size=4096)
Prot LocalAddress:Port Scheduler Flags
  -> RemoteAddress:Port           Forward Weight ActiveConn InActConn
TCP  dlp.srv.world:http wlc
  -> 10.0.0.51:http               Masq    1      0          0
  -> 10.0.0.52:http               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.

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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