Overview of impact analysis rules
The configuration management database (CMDB) captures relationships between configuration items (CIs). For example, an application RUNSON an application server. In each CI relationship, one CI is the source of the relationship, and the other CI is the target. In the example, the application CI is the source; the server is the target. Rules used by the impact analysis engine are based on these CI relationships and impact directions.
Each rule specifies a CI relationship, such as INSTALLEDON, RUNSON, or AFFECTS. Relationship names are ones that are defined for CI pairs in the configuration management database (CMDB). In addition, a rule has an impact direction (SOURCE or TARGET) that indicates which CI in a CI pair will have an outage if its related CI has an outage. Each CI relationship has a starting point, a verb, and an ending point. The starting point is the source CI; the ending point is the target CI. For example, if a payroll application REQUIRES the DB2 database, the application CI (starting point) is the source, and the database CI (ending point) is the target. When you configure rules, you specify SOURCE or TARGET as the impact direction for each relationship, which determines whether the source or the target CI in a related pair is impacted by an outage on the other CI.
The impact direction is a critically important part of an impact analysis rule. If the payroll application REQUIRES the DB2 database, the impact direction is SOURCE; this ensures that the engine identifies an impact to the SOURCE CI (payroll application) if the DB2 database is taken offline. If the payroll application is offline, the engine looks at the impact direction specified in the rule and recognizes that the DB2 database is not affected. In this relationship, only the SOURCE CI (the payroll application) is impacted by an outage.
In addition to relationships and directions, rules can have conditions that further refine the behavior of the impact assessment engine. A condition is created against the target CI or the source CI in a relationship; the rule matches only if the condition is true for that CI. For example, if you specify the target CI condition classification=app server, the rule applies only to relationship pairs in which the target CI is an application server. A condition can examine any attribute in a CI.
The engine starts with a target CI and applies the rules to calculate whether any directly related CIs are impacted. The engine then repeats this step with each identified impact, continuing to calculate impacts on related CIs to the maximum depth that is set.
The following table provides some examples of rules that you might use in your data center, along with a discussion of how each rule is applied by the impact analysis engine.
| Rule description | Relationship name | Impact direction | Discussion |
|---|---|---|---|
| Rule for Installed On | RELATION.INSTALLEDON | SOURCE | Rule: If two CIs have an INSTALLEDON
relationship, the SOURCE of the pair is impacted by an outage on the
target. For example, a payroll application is installed on a WAS Application Server. The business application CI is the source, the application server the target. The rule specifies a SOURCE impact direction, so the impact analysis engine identifies the application CI (the source) as impacted if the application server CI (the target) is taken offline. |
| Rule for Affects | RELATION.AFFECTS | TARGET | Rule: If two CIs have an AFFECTS
relationship, the TARGET of the pair is impacted by an outage on the
source. For example, a power breaker in the lab affects operation of the servers in the lab. The power breaker CI is the source, and each server is a target. The rule specifies a TARGET impact direction, so the impact analysis engine identifies each server (the targets) as impacted when the power breaker (the source) is taken out of service. |
| Rule for Runs On | RELATION.RUNSON | SOURCE | Rule: If two CIs have a RUNSON relationship,
the SOURCE of the pair is impacted by an outage on the target. For example, an e-mail application runs on the Microsoft XP operating system. The application CI is the source, and the operating system is the target. The rule specifies a SOURCE impact direction, so the impact analysis engine identifies the application (the source) as impacted if the operating system (the target) is taken offline. |
This product ships with a set of sample rules that you can use to begin running your automated impact analyses. You can use the Impact Analysis Configuration application to configure your own rules.