A BizTalk host is a logical representation of a runtime process. Each host may contain a combination of Receive or Send adapters (and their associated receive and send ports) or orchestrations.
Once you have defined a BizTalk host, you can then create instances of it. When creating an instance, you specify the name of a physical server for the host instance to execute on along with a service account for the host to run under. Hosts can be either in-process or isolated. An in-process host instance executes as a Windows service. The BizTalk tools automatically create this service when a new host is created. Isolated host instances execute in a non-BizTalk process, such as an ASP.NET worker process.
A host can have multiple instances, and this enables you to run a BizTalk host on more than one server. Furthermore, each BizTalk Server can run any combination of hosts.
Running a host on multiple boxes is important for distributing load around your BizTalk Server group. A common problem with performance testing occurs when a solution is deployed with all the adapters and orchestrations in the default BizTalkServerApplication host, due to the conflicting resource requirements of the different types of processing.
Because large parts of the BizTalk engine are written in .NET, which itself leverages the built-in CLR thread pool, if you run the SOAP adapter and your orchestrations in the same host, they will fight over limited resources, such as threads. When running multiple ...