The traditional three-tier roles of a Microsoft SharePoint Server 2010 farm can be deployed on a single server or many servers. The three-tier roles include: Web server role Application server role Database server role in a small farm, server roles can be combined on one or two servers. For example, the Web server and application server roles can be combined on a single server or on two or more servers to achieve redundancy. The Services on Server page in Central Administration lists services that are started or stopped on specific servers in the farm: Some of these services are associated with service applications. You deploy service applications by starting the associated services on the desired server computers. Some of these services are not associated with service applications. This model lists these services and indicates the server roles for which the services are recommended.
In SharePoint Server 2010, the number of services and corresponding databases is greater than in previous releases. The recommendation for scaling out a farm is to group services or databases that have similar performance characteristics onto dedicated servers and then scale out the servers as a group. For example, group all client-related services onto one or two servers and then add servers to this group as needed to satisfy user demand for these services. In some cases, you might need to create a dedicated server group for a single service, such as Excel Services or Search. This model groups service applications and related components (for example, databases) into several different logical groupings that can be used as a starting point. In large environments, the specific groups that evolve for a farm depend on the specific demands for each service.
Web frontend server
Host Web pages, Web services, and Web Parts that are necessary to process requests served by the farm. Direct requests to the appropriate application servers. This role is necessary for farms that include other SharePoint Server 2010 capabilities. In dedicated search service farms, this role is not necessary because Web servers at remote farms contact query servers directly. In small farms, this role can be shared on a server with the query component. SharePoint 2010 allows for much more granular control over the services that run and where they run by building a full (and extensible!) Service Oriented Architecture. This means that we can now utilize our Application server for almost anything including the following items:
Specific Timer Jobs - Targeted per Content Database
Service Applications - Target a much larger number of services to a specific server that we previously could in 2007
User Code Service - Isolated service for sandbox solutions
For those of us that have an existing Application Server or if you are planning your new SharePoint 2010 farm topology be sure to think about your service allocation and take better advantage of that "Application Server" role.
Application server roles
Application server roles are associated with services that can be deployed to a physical computer each service represents a separate application service that can potentially reside on a dedicated application server. Services with similar usage and performance characteristics can be grouped on a server and scaled out onto multiple servers together. For example, client-related services can be combined into a service group. After deployment, look for services that consume a disproportionate amount of resources and consider placing these services on dedicated hardware.
In a small farm environment, all databases can be deployed to a single server. In larger environments, group databases by roles and deploy these to multiple database servers