How can I ensure that an Assembly is deployed to the GAC on all Servers in a Farm

Question

I have a SharePoint Solution that contains an Assembly that contains an SPTimerJobDefinition that must be deployed to the GAC on all Servers in my farm.

I have configured my farm in the following way.

The Solution schema contains an attribute DeploymentServerType but the MSDN documentation is a little unclear on the details of what each setting means.

MSDN Solution Element (Solution)

My experiments have shown that a value of WebFrontEnd causes the Assembly to be deployed to only my Central Admin and Web Front End Server. This seems logical to me.

In Visual Studio 2010 I changed the setting to ApplicationServer and observed that the Assembly was now deployed to all my servers (Web Front End,Central Admin and Application Server) This was not expected by me I expected it to deploy to only the Application Server and NOT to Central Admin and the Web Front End.

Is this the expected behavior of DeploymentServerType=ApplicationServer? Is there an error in my farm configuration that is causing this to occur by accident?

Update

My "Web Front End" server seems to think it is an Application server.

PS C:\> [Microsoft.SharePoint.Administration.SPServer]::Local | select Name,Role

Name                    Role
----                    ----
SIFI-CAT-TST4           Application

Is this normal?

Update

I have a server I installed as StandAlone and it reports it is a SingleServer

PS C:\> [Microsoft.SharePoint.Administration.SPServer]::Local | select Name,Role

Name                    Role
----                    ----
SIFI-SP-SPDEV2          SingleServer

Answer 1

This field is optional and if you do not specify anything, your assembly should be installed in GAC on all servers. Again, this is based on my reading of other users' experience here: http://social.msdn.microsoft.com/Forums/en/sharepointdevelopment/thread/03c35630-0f68-44bc-a097-44a77c6c21dd

SPServer.Role is weird, my development server (everything on one box) is showing "Application" too. Based on enumeration values, I would expect "SingleServer". My best "guess" that this value is determined when SharePoint Components are installed and potential of server. If I had selected "StandAlone" during installation, I would see a value of "SingleServer" (Users, please confirm the value if you had stand-alone installation)

Also, the role is determined by Registry key HKLM\Software\Microsoft\Shared Tools\Web Server Extensions\14.0\WSS, I would doubt if this value gets updated as you switch roles.