HAproxy is open source proxy that can be used to enable
high availability and
load balancing for web applications. It was designed especially for high load projects so it is very fast and predictable, HAProxy is based on single-process model.
In this post I’ll describe sample setup of HAProxy: users’ requests are load balanced between two web servers
Web1 and
Web2, if one of them goes down then all the request are processed by alive server, once dead servers recovers load balancing enables again. See topology to the right.
Installation
HAProxy is included into repositories for major Linux distributions, so if you’re using
Centos,
Redhat or
Fedora type the following command:
#yum install haproxy
If you’re Ubuntu, Debian or Linux Mint user use this one instead:
#apt-get install haproxy
Configuration
As soon as HAProxy is installed it’s time to edit its configuration file, usually it’s placed in
/etc/haproxy/haproxy.cfg.
Official documentation for HAProxy 1.4 (stable) is
here.
Here is configuration file to implement setup shown at the diagram and described above:
global
user daemon
group daemon
daemon
log 127.0.0.1 daemon
listen http
bind 1.2.3.4:80
mode http
option tcplog
log global
option dontlognull
balance roundrobin
clitimeout 60000
srvtimeout 60000
contimeout 5000
retries 3
server web1 web1.hackerschronicle.com:80 check
server web2 web2.hackerschronicle.com:80 check
cookie web1 insert nocache
cookie web2 insert nocache
Let’s stop on most important parts of this configuration file. Section
global specifies user and group which will be used to run haproxy process (
daemon in our example). Line
daemon tells HAProxy to run in background,
log 127.0.0.1 daemon specifies syslog facility for sending logs from HAProxy.
Section
listen http contains line
bind 1.2.3.4:80 that specifies IP address and port that will be used to accept users’ requests (they will be load balanced between Web1 and Web2). Line
mode http means that HAProxy will filter all requests different from HTTP and will do load balancing over HTTP protocol.
Line
balance roundrobin specifies load balancing algorithm according to which each web server (Web1 and Web2) will be used in turns according to their weights. In our example weights for both servers are the same so load balancing is fair.
Lines
server web1 … and
server web2 … specify web servers for load balancing and failover, in our case they are load balanced according to round robin algorithm and have the same priority/weight.
The last two lines in configuration files are optional, they makes it possible to preserve cookies, it means for example that if you logged in to web application hosted at Web1 and then HAProxy forwarded your next request to Web2 you will still have logged in session opened as cookies with session id from Web1 will be sent to you from Web2 as well.
you have successfully configured HAProxy load balancer. Read next article to
.