HAProxy Load Balancer

Introduction

Load Balancing is a technique to spread work between two or more computers, network links, CPUs, hard drives, or other resources, in order to get optimal resource utilization, maximize throughput, and minimize response time.

Load balancer is a tool that directs a client to the least busy or most appropriate Web server among several servers that contain mirrored contents.

Why is load balancing of servers needed?

The web server may not be able to handle high volumes of incoming traffic.

The users will have to wait until the web server is free to process their requests.

There may be a situation where upgrading the server hardware will no longer be cost effective.

Load-balancing techniques

Three types of load balancers exist:Hardware appliancesNetwork switchesSoftware

Load-balancing techniques

A hardware appliance-based load balancer is a closed box.

A network switch-based load balancer uses a Layer2 or Layer3 switch to integrate the load-balancing service.

A software load balancer is software which you can install on a dedicated server.

How to achive load balancing?

More servers need to be added to distribute the load among the group of servers, which is also known as a server cluster.

The load distribution among these servers is known as load balancing.

Load balancing applies to all types of servers (application server, database server).

Software Load Balancers

1.Haproxy2.Pure Load Balancer (PLB)3.Perlbal4.Pound5.Pen

Haproxy Load Balancer

HAProxy is a free, very fast and reliable solution offering high availability, load balancing, and proxying for TCP and HTTP-based applications.

Installation

$ apt-get install haproxyDownload the HAProxy (http://haproxy.1wt.eu/#down)

Untar the downloaded file.$ ./configure$ make$ make install

HAProxy Status

Examples

http://www.mobshare.in

listen webfarm 192.168.1.1:80 mode http balance roundrobin cookie SERVERID insert indirect option httpchk HEAD /index.html HTTP/1.0 server webA 192.168.1.11:80 cookie A check server webB 192.168.1.12:80 cookie B check port 81 inter 2000 server webC 192.168.1.13:80 cookie C check server webD 192.168.1.14:80 cookie D check server bkpA 192.168.1.15:80 cookie A check backup server bkpB 192.168.1.16:80 cookie B check backup

http://www.mobshare.in

http://www.mobshare.in

Updating...

503 Service UnavailableNo server is available to

handle this request.

Load balancing algorithms

round-robin: requests are rotated among the servers.

leastconn: the request is sent to the server with the lowest number of connections.

source: a hash of the source IP is divided by the total weight of the running servers to determine which server will receive the request.

Load balancing algorithms...

uri: the part of the URL up to a question mark is hashed and used to choose a server that will handle the request.

url_param: can be used to check certain parts of the URL, for example values sent via POST requests; for example a request which specifies a user_id parameter with a certain value can get directed to the same server using the url_param method.

Basic Configuration

The configuration file haproxy.cfg is segmented in sections. global section listen section default section

OR global section default section frontend section backend sections

Global Section Example

global daemon quiet nbproc 2 pidfile /var/run/haproxy-private.pid

user haproxy group public

Default Section Example

defaults log global mode http option httplog option forwardfor

Listen Section Example

listen webfarm 192.168.1.1:80 mode http balance roundrobin cookie SERVERID insert indirect option httpchk HEAD /index.html HTTP/1.0 server webA 192.168.1.11:80 cookie A check server webB 192.168.1.12:80 cookie B check server webC 192.168.1.13:80 cookie C check server webD 192.168.1.14:80 cookie D check

Frontend Section Example

frontend myfrontend *:80log globalmaxconn 25000option forwardforacl acl_example1 url_sub example1acl acl_example2 url_sub example2use_backend example1_farm if acl_example1use_backend example2_farm if acl_example2default_backend default_farm

Backend Sections Example

backend example1_farmmode httpbalance roundrobinserver server1 192.168.1.1:80 checkserver server2 192.168.1.2:80 check

backend example2_farmmode httpbalance roundrobinserver server3 10.0.0.3:80 checkserver server4 10.0.0.4:80 check

backend default_farmmode httpbalance roundrobinserver server5 192.168.1.5:80 checkserver server6 192.168.1.6:80 check