SharePoint Programming

Concept : When you create a service application in Microsoft SharePoint Server 2010,
a service application connection is created. A service application connection is also referred to
as an application proxy. Each Service Applications have a corresponding Service Application Proxy.

A service application connection or proxy associates the service application to a Web application( after adding the service application connection in web application's custom connection group). This association is controlled through the use of Service application Proxy Groups(or web app's custom connection group or farms' default connection group). Proxy Groups create mappings between service applications proxies and the web applications that consume them.


Note : By default, a new service application connection is added to the farm’s Default group of service application connections when you create the service application by using Central Administration. You can override this default membership.
If a new service application is created by using Windows PowerShell 2.0 instead of by using Central Administration, the new service application does not automatically
become a member of the Default service application connections group unless the -default parameter is supplied.

By default, all Web applications are associated with the farm’s Default group of service application connections, although you can change this setting and can also create one custom connection group for each Web application in the farm.


That means,
For e.g. A single web application can consume multiple search shared services, and A single shared service can be consumed by multiple web applications.

To Associate a Service Application to a Web application, you just need to add it to a custom service application connection group.

Add -SPServiceApplicationProxyGroupMember [-Identity connGroup ] [-Member serviceapp ]

To Remove a service application connection from a service application connection group

Remove-SPServiceApplicationProxyGroupMember [-Identity connGroup ] [-Member serviceapp ]

Note : The group could be default Farm's group or could be a custom service application connection group for a webapplication.Rules

Some additional Notes:

1. A web application can only map to one proxy group by default

2. A service application can map to one or more proxy groups. Another way of saying multiple proxy groups can contain the same service application proxy

3. A proxy group can contain multiple service applications of the same type. So it's possible to have two Excel Service Applications reside in the same proxy group.


Ref : Service Applications