What is Central Administration, WFE and Application Server in SharePoint?

Central Administration (CA)

• Central Administration is the management tool for your whole farm.
• When you install and configure SharePoint Products and Features (SharePoint Foundation, or SharePoint Server etc.) on any application server, it automatically provisions a central administration site on that server.
• Typically Central Administration is hosted on Application server. When the service “Central Administration” is running on any application server, that server hosts site for Central administration for the whole farm.
• CA is kept on application server as it is not a high traffic site and won't affect performance of the application server.
• It also allows you to extract a level of security by not putting it on a web front end, which could be accessed via a load balancer, instead it's on server that's behind the scenes that less users would even know about.
• CA is an admin only site that has the potential to completely destroy your entire farm if misused or hacked. In many farms, particularly Internet/Extranet farms, the WFEs are exposed to the internet and are thus subject to being hacked. If CA isn't installed on a WFE, it eliminates the potential that a hacker will gain access to it.
• On the server that is running SharePoint Products, click Start, point to Administrative Tools, and then click SharePoint Central Administration.

     

    Web Front End Servers (WFE server)

•  A “Web Front End” (WFE) is a server where only “WSS/SharePoint Foundation Web Application” service is running from the below table “Server services”.
• A WFE handles web requests from users and hosts all SharePoint files on the disk.
• The assemblies are deployed to the global assembly cache (GAC) of every front-end web server in the farm and run with full trust.
• A WFE has all the web applications (in IIS), Assembly in GAC and SharePoint related files in 12/14/15 hive.
• You can have more than one WFE for load balancing (just install a secondary WFE in the Farm).

 Application Server (App server)

•  An “Application Server” is a server that is capable of running any of the services from table below apart from the “WSS/SharePoint Foundation Web Application” service.
• Application server hosts services such as: Excel, Search etc. and you can have one or more application servers in the farm for scalability and balancing.
• You could split Excel and Search on two different servers (application) in the farm.
• SharePoint will not replicate contents of WSP on app server as the “WSS/SharePoint Foundation Web Application” service is turned off there.

Server Services (MOSS version)

Server Service	Purpose
Windows SharePoint Services Web Application (often referred to as 'Web Server' or 'WFE')	This service is responsible for serving the HTML to clients and routing requests to other services in the farm. This service can exist on multiple servers. Those servers are called as WFE servers.
Office SharePoint Server Search in Query Mode (often referred to as 'Query Server')	This service is responsible for executing search queries against a locally stored copy of the index Yes, this role can exist on multiple servers.
Office SharePoint Server Search in Index Mode (often referred to as 'Index Server')	This service is responsible for indexing all of the configured content sources, creating an index and propagating it to every Query server in the farm
Windows SharePoint Services Search	This service is basically a slimmed down version of the Office SharePoint Server Search service which combines both the Query and Index roles into a single service. If you have more than one instance of this service in a farm, it will simply do the same thing as the other servers.
Excel Calculation Services	This service is responsible for performing calculations on Excel workbooks that are stored in the content databases. Many instances of this service can exist on the same farm.
Document Conversions Load Balancer Service	This service balances document conversion requests from across the server farm. An application server can only have a single Document Conversions Load Balancer Service enabled.
Document Conversions Launcher Service	This service schedules and initiates the document conversions on a server. Multiple launchers can exist in the same farm.
Windows SharePoint Services Incoming E-Mail	This service is responsible for receiving incoming emails and placing them in email enabled lists.  This service can run on multiple servers
Windows SharePoint Services Outgoing E-Mail	This is not technically a SharePoint service but refers to an SMTP server which SharePoint send outbound email to
Central Administration	This service enables the central administration interface that is required for farm-wide administration. This service can only run on one server in the farm i,e. on any single Application server.

How Solution (.wsp) is deployed to SharePoint farm?

• WSP Solution can be deployed with PowerShell script using commands Add-SPSolution and Install-SPSolution.
• Add-SPSolution will move your solution to SP Admin database.
• Install-SPSolution will create a timer job on all WFE’s to push all files to 12/14/15 hive, DLL's to GAC, Web.Config changes etc. to the Front end servers where you have "SP Web Application" service running.
• It doesn’t matter which server you are using to deploy your WSP with PowerShell. It can be Application server or WFE server.
• The solution functionalities will be always executed on your front end server, your app server doesn’t need the WSP artifacts.