Configuring Nginx as a Load Balancer

Before to start we need to have 3 servers with AlmaLinux 8 installed and configured with the following IP addresses:

• Server One: x.x.x.160
• Server Two: x.x.x.161
• Server Three: x.x.x.162

On each server we need to install Nginx and configure the firewall to allow HTTP and HTTPS traffic:

dnf install nginx -y
firewall-cmd --add-service=http --permanent
firewall-cmd --add-service=https --permanent
firewall-cmd --reload

Now we need to configure another server with Nginx as a load balancer. To do this we need to edit a file /etc/nginx/conf.d/filename.conf and add the following lines:

log_format backendlog '$remote_addr - $remote_user [$time_local] "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent"';

upstream backend {
    server x.x.x.160;
    server x.x.x.161;
    server x.x.x.162;
}

server {
    listen 80;

    access_log /var/log/nginx/loadbalancer.access.log backendlog;

    location / {
        proxy_pass http://backend;
    }
}

After that we need to restart the Nginx service:

systemctl restart nginx

If you want to persist sessions between requests, you can use the ip_hash directive in the upstream block:

upstream backend {
    ip_hash; # <--- Add this line
    server x.x.x.160
    server x.x.x.161
    server x.x.x.162
}

If you want to send request to the server that has the least number of active connections, you can use the least_conn directive in the upstream block:

upstream backend {
    least_conn; # <--- Add this line
    server x.x.x.160
    server x.x.x.161
    server x.x.x.162
}

Note: Sometimes you might notice that a 502 bad gateway error appears when you try to access to the load balancer server. To avoid this problem, just disable SELinux on the load balancer server.

setenforce 0