Install HAProxy Load Balancer on CentOS

Install HAProxy Load Balancer on CentOS

Understand about High Available (HA) and Load Balancing

Configuring the load balancer

Setting up HAProxy for load balancing is a quite straight forward process. Basically all you need to do is tell HAProxy what kind of connections it should be listening for and which servers it should relay the connections to. This is done by creating a configuration file /etc/haproxy/haproxy.cfg with the defining settings. You can read about the configuration options at HAProxy documentation if you wish to find out more.

Open a .cfg file for edit for example using vi with the following command

sudo vi /etc/haproxy/haproxy.cfg

Add the following sections to the the file. Replace the  with what ever you want to call you servers on the statistics page and the > with the private IPs for the servers you wish to direct the web traffic to. You can check the private IPs at your UpCloud Control Panel and Private network -tab under Network -menu.

global
   log /dev/log local0
   log /dev/log local1 notice
   chroot /var/lib/haproxy
   stats socket /run/haproxy/admin.sock mode 660 level admin
   stats timeout 30s
   user haproxy
   group haproxy
   daemon

defaults
   log global
   mode http
   option httplog
   option dontlognull
   timeout connect 5000
   timeout client 50000
   timeout server 50000

frontend http_front
   bind *:80
   stats uri /haproxy?stats
   default_backend http_back

backend http_back
   balance roundrobin
   server  :80 check
   server  :80 check

This defines a layer 4 load balancer with a front-end name http_front listening to the port number 80, which then directs the traffic to the default back-end name http_back. The additional stats uri /haproxy?stats enables the statistics page at that specified address. Configuring the servers in the back-end section allows HAProxy to use these servers for load balancing whenever available according to the roundrobin algorithm.

The balancing algorithms are used to decide which server at the back-end each connection is transferred to. Some of the useful options include the following:

• Roundrobin: Each server is used in turns according to their weights. This is the smoothest and fairest algorithm when the servers’ processing time remains equally distributed. This algorithm is dynamic, which allows server weights to be adjusted on the fly.
• Leastconn: The server with the lowest number of connections is chosen. Round-robin is performed between servers with the same load. Using this algorithm is recommended with long sessions, such as LDAP, SQL, TSE, etc, but it’s not very well suited for short sessions such as HTTP.
• First: The first server with available connection slots receives the connection. The servers are chosen from the lowest numeric identifier to the highest, which defaults to the server’s position in the farm. Once a server reaches its maxconn value, the next server is used.
• Source: The source IP address is hashed and divided by the total weight of the running servers to designate which server will receive the request. This way the same client IP address will always reach the same server while the servers stay the same.

An other possibility is to configure the load balancer to work on layer 7, this can be useful when parts of your web application are located on different hosts. This can be accomplished by conditioning the connection transfer for example by the URL.

frontend http_front
   bind *:80
   stats uri /haproxy?stats
   acl url_blog path_beg /blog
   use_backend blog_back if url_blog
   default_backend http_back

backend http_back
   balance roundrobin
   server  :80 check
   server  :80 check

backend blog_back
   server  :80 check

The front-end declares an ACL -rule named url_blog that applies to all connections which path begins with /blog, and use_backend defines that connections matching the url_blog condition should be served by the back-end named blog_back.

At the back-end side the configuration sets up two server groups, http_back like before and the new one called blog_back that servers specifically connections to domain.com/blog.

After making the configurations, save the file and restart HAProxy with the following

sudo systemctl restart haproxy

If you get any errors or warnings at start up, check the configuration for any mistypes and that you’ve created all the necessary files and folders, then try restarting again.

Configuring the High Available - HA

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defaults  mode http  option http-server-close  timeout client 20s  timeout server 20s  timeout connect 4s frontend ft_app  bind 10.0.0.100:80 name app  default_backend bk_app backend bk_app  server s1 10.0.0.1:80 check  server s2 10.0.0.2:80 check backup