The process of creating a multiple-machine deployment of ArcGIS Server has also been simplified. You run the same installation on each machine and connect the machines using ArcGIS Server Manager.
Opening Manager the first time
When you open Manager the first time, you'll be asked whether you want to create a new site or join an existing site. Creating a new site means you are just getting started and you want to add this machine as the first GIS server in your configuration. Joining an existing site means that you want to add this machine as a GIS server in an existing configuration. See the help topics below to learn what you'll need to do for the option you choose:
A site is a deployment of ArcGIS for Server. If you've installed ArcGIS for Server for the purpose of connecting it to an existing site, you have the opportunity to specify that site the first time you open Manager.