Category: Load Balancers

Load balancing applications across multiple servers is a common technique for creating highly available, fault-tolerant solutions. Nginx can serve as a very light weight and efficient HTTP load balancer to distribute traffic to multiple servers.

This guide will outline one basic way Nginx can be deployed as a load balancer.

Install Nginx

First, install Nginx on your server. In many cases, the version of Nginx supplied by the OS repos is outdated, so this guide will be using Nginx’s official repos instead.

# CentOS 6
[root@lb01 ~]# rpm -i http://nginx.org/packages/centos/6/noarch/RPMS/nginx-release-centos-6-0.el6.ngx.noarch.rpm
[root@lb01 ~]# rpm --import http://nginx.org/keys/nginx_signing.key
[root@lb01 ~]# yum install nginx
[root@lb01 ~]# chkconfig nginx on

# CentOS 7
[root@lb01 ~]# rpm -i http://nginx.org/packages/centos/7/noarch/RPMS/nginx-release-centos-7-0.el7.ngx.noarch.rpm
[root@lb01 ~]# rpm --import http://nginx.org/keys/nginx_signing.key
[root@lb01 ~]# yum install nginx
[root@lb01 ~]# systemctl enable nginx

# Ubuntu 14.04 and 16.04
[root@lb01 ~]# nginx=stable # use nginx=development for latest development version
[root@lb01 ~]# apt-get install python-software-properties
[root@lb01 ~]# add-apt-repository ppa:nginx/$nginx
[root@lb01 ~]# apt-get update
[root@lb01 ~]# apt-get install nginx

Create Load Balancer config

As I have many servers running different domains, I will be setting up Nginx to load balance specific domains to specific servers. So in the example below, www.example.com will be load balanced to my 2 servers, 192.168.1.161 and 192.168.1.162.

The notable things defined in this example include:

- Uses Least Connections for routing traffic to the load balanced web servers
- Servers will automatically be disabled in the load balancer
- The load balancer will pass the x-forwarded-for header (real IP) to the load balanced web servers

Create the config by:

[root@lb01 ~]# vim /etc/nginx/conf.d/example.com.conf
upstream lb-example.com {

	# Load balancing method, only enable one.
	# blank        # Round robin, leave commented out as it is the default
        least_conn;    # Least connections
	# ip_hash;     # Sticky sessions 

	# Backend load balanced servers
        server 192.168.1.161 max_fails=3 fail_timeout=15s;
        server 192.168.1.162 max_fails=3 fail_timeout=15s;

	# Temporarily disable server in load balancer
        # server 192.168.1.163 down;
}

server {
        listen 80;
        server_name www.example.com example.com;
        access_log  /var/log/nginx/example.com.access.log  main;
        # Enforce https
        # return 301 https://$server_name$request_uri;
        # }

        # Pass to load balanced servers
        location / {
        proxy_pass http://lb-example.com;
	
	# Pass x-forwarded-for headers to backend servers
	proxy_set_header Host $host;
	proxy_set_header X-Real-IP $remote_addr;
	proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
	proxy_set_header X-Forwarded-Proto $scheme;
        }
}

server {
        listen 443 ssl;
        server_name www.example.com example.com;
        access_log  /var/log/nginx/example.com.access.log  main;

        location / {
        proxy_pass https://lb-example.com;

        # Pass x-forwarded-for headers to backend servers
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
        }
}

Now test the new configuration to ensure there are no errors and restart nginx:

[root@lb01 ~]# nginx -t
[root@lb01 ~]# service nginx restart

Ensure that you open the software firewall for 80 and 443 accordingly. Below is an example for CentOS 6:

[root@lb01 ~]# vim /etc/sysconfig/iptables
...
-A INPUT -p tcp --dport 80 -j ACCEPT
-A INPUT -p tcp --dport 443 -j ACCEPT
...
[root@lb01 ~]# service iptables restart