About server object container (SOC) machines
Server object container (SOC) machines host services and are the work centers of your GIS server. For your GIS server to utilize these SOC machines, you need to link them to the server object manager (SOM). When you install all the components of ArcGIS Server on one machine, the SOC is automatically linked to the SOM, and you don't have to take any further action. If you install the components of ArcGIS Server across multiple machines, then you need to manually add the SOC as described below.
For a machine to function as a SOC, it needs to have the Server Object Container component of ArcGIS Server installed on it.
Additionally, on the Windows platform, you should run the GIS Server Post Install on the container machine, specifying the same SOM account and SOC account names and passwords that you use on all the other machines of your ArcGIS Server system.
On Linux/Solaris, before adding a SOC machine, you should add the install owner, which is also the SOC account, to the Local GIS user list in Manager.