The simplest method with NGINX to do load balancing is to have two webservers serving both the same content and have them act equally in a cluster. To achieve this you need to define the servers in the cluster and then let the proxy_pass definition point to the cluster definition.

A cluster is defined using the upstream section within the HTTP section like this 

 

upstream main {
        server 192.192.23.92:80 weight=30;
        server 192.192.23.93:8000;
}  

And you can point to it in the server section like this:

server {

  listen 192.192.23.189:80 

  location / {

    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_pass http://main; 

  }

}

As you can see from above, you can provide a weight, describing which server should get the higher load.

You can control the behavior of the proxy and when and how it treats the webserver down / hanging with the proxy_*_timeout settings. These settings are per server, but can also be given per location

   server {

       # default:
       #proxy_next_upstream  error timeout invalid_header;

       
       proxy_connect_timeout   5;
       proxy_send_timeout      5;
       proxy_read_timeout      15;


       location  /longreportpage  {
           proxy_pass     ...

           proxy_connect_timeout   5;
           proxy_send_timeout      5;
           proxy_read_timeout      60;
       }
    }

The example above is used for a server which occasionally hangs (like AOLserver has the tendency to do). The connect_timeout is used to determine how long we wait for a connection to come back. The read timeout determines, once a connection has been established, how long the pages may take to be delivered fully.

This is why we have (for a report page that takes up a long time) a longer read_timeout, as the report takes longer on the server to finish.

Load balancing OpenACS

If you are load balancing OpenACS here are a couple of things to keep in mind:

• Use OpenACS 5.4. Previous versions do not have support for dynamic sitemaps 
• Configure the cluster section in the acs-kernel parameters. Namely:
  • CanonicalServer: Which is the mainserver (192.168.23.92) 
  • ClusterEnabled: Should be 1
  • ClusterPeerIP and ClusterAuthorizedP: Should be all servers from above 
• Make sure to use permission caching
  • Make sure none of your custom packages use acs_permission__grant or acs_permission__revoke calls in PL/SQL and that you do not insert into acs_permissions directly (or delete from it). This is bad coding anyways with the new standards.
  • Turn on PermissionCacheP in the acs-kernel parameters by setting it to "1"
  • Once done, restart your server.