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Chapter 8. Rules

Table of Contents

8.1. Rule Properties
8.2. Node Attribute Expressions
8.3. Time- and Date-Based Expressions
8.3.1. Date Specifications
8.3.2. Durations
8.3.3. Sample Time-Based Expressions
8.4. Using Rules to Determine Resource Location
8.4.1. Location Rules Based on Other Node Properties
8.4.2. Using score-attribute Instead of score
8.5. Using Rules to Control Resource Options
8.6. Using Rules to Control Cluster Options
8.7. Ensuring Time-Based Rules Take Effect
Rules can be used to make your configuration more dynamic. One common example is to set one value for resource-stickiness during working hours, to prevent resources from being moved back to their most preferred location, and another on weekends when no-one is around to notice an outage.
Another use of rules might be to assign machines to different processing groups (using a node attribute) based on time and to then use that attribute when creating location constraints.
Each rule can contain a number of expressions, date-expressions and even other rules. The results of the expressions are combined based on the rule’s boolean-op field to determine if the rule ultimately evaluates to true or false. What happens next depends on the context in which the rule is being used.

8.1. Rule Properties

Table 8.1. Properties of a Rule

Field Default Description
Limits the rule to apply only when the resource is in the specified role. Allowed values are Started, Slave, and Master. A rule with role="Master" cannot determine the initial location of a clone instance and will only affect which of the active instances will be promoted.
The score to apply if the rule evaluates to true. Limited to use in rules that are part of location constraints.
The node attribute to look up and use as a score if the rule evaluates to true. Limited to use in rules that are part of location constraints.
How to combine the result of multiple expression objects. Allowed values are and and or.