by Andrew Johnstone
In: Linux14 Jun 2009
Recently we had an issue with one of our hosting providers load balancing (LVS), which resulted in some very small outages. As a result we decided to setup our own load balancing that we had full control over, and could manage ourselves. In addition to choosing a better suited weighting algorithm.
Each webserver is setup using ucarp an implementation of Common Address Redundancy Protocol (CARP) allowing failover of a single Virtual IP (VIP) for high availability. We bound multiple VIPs for each host as we noticed some HTTP 1.0 clients incorrectly sending the host address to the server.
In order to setup ucarp & haproxy:
apt-get install -y haproxy ucarp
Modify /etc/network/interfaces giving each interface a unique ucarp-vid and adjust ucarp-advskew for weighting on each server (increment by one for each server) and set ucarp-master to yes if it is to be the master. Modify the configuration below appropriately.
# The primary network interface auto eth0 iface eth0 inet static address 10.10.10.2 # IP address of server netmask 255.255.255.255 broadcast 10.10.10.10 gateway 10.10.10.1 ucarp-vid 3 ucarp-vip 10.110.10.20 # VIP to listen to ucarp-password password ucarp-advskew 10 ucarp-advbase 1 ucarp-facility local1 ucarp-master yes iface eth0:ucarp inet static address 10.10.10.20# VIP to listen to netmask 255.255.255.255
To bring the interface up, simply run the following:
ifdown eth0; ifup etho0 ifdown eth0:ucarp; ifup eth0:ucarp
In order to configure haproxy:
sed -i -e 's/^ENABLED.*$/ENABLED=1/' /etc/default/haproxy
Reconfigure apache to listen only on local interfaces (/etc/apache2/ports.conf):
So replace “Listen 80″ with
Listen 10.10.10.20:80 Listen 10.10.10.2:80
listen web 10.10.10.20:80 mode http balance leastconn stats enable stats realm Statistics stats auth stats:password stats scope . stats uri /stats?stats #persist server web1 10.10.10.2:80 check inter 2000 fall 3 server web2 10.10.10.3:80 check inter 2000 fall 3 server web3 10.10.10.4:80 check inter 2000 fall 3 server web4 10.10.10.5:80 check inter 2000 fall 3 server web5 10.10.10.6:80 check inter 2000 fall 3
Then restart haproxy with /etc/init.d/haproxy restart
Carp & HA Load Balancing
After changing your DNS to point to 10.10.10.20 you will be able to see the traffic balanced between the servers by going to the URL http://10.10.10.20/stats?stats with the credentials assigned above and see the bytes balanced between the servers listed.
Some other alternatives are:
Andrew Johnstone is a software engineer / lead developer working at Everlution Software.