Plesk Sitebuilder is based on layered architecture and supports several deployment scenarios in which system components may be distributed on multiple physical tiers. In terms of application deployment, components are grouped into logical tiers which form the deployment units. As shown in Figure 1, multi-tiered deployment architecture consists of Data, Storage and Application tiers.
Data tier consists of SQL Server database, which stores application business entities such as user accounts, sites, and system settings.
Storage tier consists of file-based Repository components providing persistence service for user sites and their building blocks such as design templates, page sets and modules.
Application tier is composed of Web-based front-end application and Windows Service that are integrated with Internet Information Services (IIS). Web application provides user interface (UI) for the end users and system administrators and also exposes several Web Services for integration and remote administration. Preview hosting service provides design time IIS hosting for the user web sites and manages their life time.
You can install the logical tiers of the Plesk Sitebuilder server on one or more physical computers. In the context of this guide we will consider multi server deployment. Figure 2 shows typical implementation of Web Farm based on Network Load Balancing (NLB) clusters. For details of how to implement NLB cluster, see the deployment guide at Microsoft web site. Additional details regarding IIS scalability with Network Load Balancing may be found at Microsoft web site.
Web farm network segment represents NLB cluster consisting of two or more computers with NLB enabled network adapters. Application tier should be deployed on each web farm server which is part of virtual Plesk Sitebuilder cluster (within a single physical cluster there might be several virtual clusters distinguished by cluster address).
Important: NLB cluster should be configured to use a single client affinity to guaranty correct operations of Plesk Sitebuilder application tier components.
Storage and Data tiers reside within the private LAN segment. They might be deployed to storage and database servers correspondingly or installed on one computer. Though from the beginning it might be enough to have a single server with RAID 5 disk system for both storage and database tiers, it's recommended to deploy these tiers to different computers in order to be able to scale out the machines independently on demand to load growth.
To increase availability of the storage server, you may install the storage tier on several machines and then setup Distributed File System (DFS) with File Replication Service (FRS). If you decide to do so, you should manually configure DFS and FRS services; for details, see the guide at Microsoft web site.
To increase availability of the database server, you may implement failover SQL Server 2005 cluster; for details, see the guide at Microsoft web site.