iIS Process Engine Components
Chapter 1 Introduction: iIS Process Management 31
iIS Process Engine Components
As mentioned earlier in this chapter, an iIS process engine is the heart of an iIS
system and has been designed to support mission-critical production application
systems. The iIS process engine maintains performance under heavy and/or
increasing loads and provides automatic recovery in case of unanticipated system
failure.
To support both failover and load balancing, the iIS process engine is engineered as
a set of interacting application components. These applications work together to
provide engine failover protection and the flexibility to handle increasing loads. An
iIS engine generally consists of the following application components:
•two engine units
•an engine governor
•a number of database access services
An iIS engine also includes a database that provides storage for persistent state
information.
The various engine components are described below in relation to their role in
providing failover and load balancing capability. A minimal engine configuration
is discussed first, followed by failover and load balancing configurations. To create
these configurations, see “Configuring an Engine” on page 85.

Minimal Engine Configuration

An iIS process engine consists minimally of three components—an engine unit, a
database service, and a database—as shown in Figure1-2. In this configuration, the
engine provides basic functions without failover or load balancing capabilities.