A host is a container for other BizTalk entities, including orchestrations and receive and send handlers. Thus, a host can be configured to perform activities such as receiving, processing, and sending messages. There are two types of hosts:
· In-Process host - This kind of host runs within the memory space of the BizTalk service. The File, SMTP, FTP, and SQL adapters all run in this kind of host. An In-Process host can be used for receiving messages, sending messages, and processing orchestrations.
· Isolated host - As the name suggests, this type of host runs within its own memory space, which means that a separate process will be created to run such a host. Good examples are the SOAP and HTTP adapters. These adapters run under a worker process (W3P.exe) created by IIS. The BizTalk Service does not control this type of host. An isolated host can be used for receiving and sending messages, but not for processing messages in orchestrations.
If a scenario demands high performance, it is usually helpful to create different hosts for receiving, processing, and sending messages. Dedicating a host for each of these three activities essentially decouples their work queues, which helps BizTalk efficiently partition the work. This topic is explored in more detail later in the chapter.
Additionally, it can be useful to create multiple hosts for the purpose of setting up security boundaries. Different hosts can be run under different security contexts, which can be very useful when a BizTalk solution demands messaging interactions with external trading partners.
A host instance is the actual BizTalk Service that runs on a physical BizTalk server machine. This service comprises XLANG, MSMQT, TDDS, and BizTalk Messaging Service. These sub-services are not visible to the administrator. The default installation of BizTalk Server 2004/2006 creates one BizTalk Service (BizTalk Server Application BTSNTSvcs.exe).
You need to consider the following guidelines when you create hosts and host instances.
· A BizTalk Server can hold multiple hosts.
· A host can hold multiple host instances.
· The act of mapping a host to a BizTalk Server creates a host instance.
· A host can be mapped to one or more BizTalk Servers.
· A host can register only one host instance of a specific server.
*** NOTE ***
The above content is excerpted from “Microsoft BizTalk Server 2004 Unleashed” book, By Scott Woodgate, Stephen Mohr, Brian Loesgen, Susie Adams, Alex Cobb, Benjamin Goeltz, Brandon Gross, Chris Whytock, Erik Leaseburg, Gavin Islip, Imran Aziz, Kevin Smith, Michael Roze, Naveen Goli, Puru Amradkar, Stephen Roger.
The following article further shows you how to add a new host and host instance step by step.
BizTalk Server 2004 - Hosts & Host Instances, by Jeff Lynch
http://codebetter.com/blogs/jeff.lynch/archive/2005/02/21/51307.aspx
