Load balancing (LOAD BALANCING) optimizes processing speed (4 layers).

Load balancing helps the server handle a large number of requests.

As usual, the request from the client goes directly to a single web server, this can cause server congestion, slow processing speed.



Load balancing will be based on algorithms depending on need to control other web servers.



There are 3 types of load balancing algorithms:

  • Round robin : this method selects servers sequentially. The load balancer will select the first server in its list for the first request, then move down to the next server in the list in order and start from the beginning when the list is exhausted.
  • Least connection : The load balancing system will choose the server with the fewest connections and this method is recommended when access speed is slow.
  • Source : with the Source algorithm, the load balancer selects the server based on a sequence of origin IPs of the request, such as the visitor’s IP. This method ensures that a particular user will always connect to the same server.


Load balancing includes 2 types:

  • Hardware: Uses hardware to control the request. Devices such as: Foundry, Nortel (Alteon) or Cisco CSS (Arrowpoint), Cisco Local Director…
  • Software: Use software to handle requests. Software such as: Nginx, Haproxy, Apache ….


Load balancing includes 2 models: 4 layers and 7 layers.

Here’s how to install 4-layer Soft Load Balancer and use Haproxy:



  • Load Balancer
    OS: CentOS 7 + haproxy
    Private IP:
  • Web Server 1
    OS: CentOS 7 + Nginx
    Private IP: 192.168.129:8080
  • Web Server 2
    OS: CentOS 6+ Nginx
    Private IP: 192.168.128:80

At the Load Balancer and Web Server 1, open ports 80 and 8080. At Web Server 2, open port 80. Web Server 1 will have the content ‘a,’ and Web Server 2 will have the content ‘b.’

Install Haproxy on Load Balancer

sudo yum install haproxy

Then edit the file /etc/haproxy/haproxy.cfg. Make a backup of this file.

 maxconn 256

 mode http
 timeout connect 5000ms
 timeout client 50000ms
 timeout server 50000ms

 stats enable
 stats hide-version
 stats refresh 30s
 stats show-node
 stats auth admin:123456
 stats uri /haproxy?stats

frontend http-in
 bind *:80
 default_backend servers

backend servers
 balance roundrobin
 server webserver1 check
 server webserver2 check


Run command sudo service haproxy start

Type in the url and you will see the content change to “a” and “b”.

To see information about web servers we access with the account admin/123456


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