Chapter 8. Rules

Table of Contents

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.

Table 8.1. Properties of a Rule

Field	Description
`role`	Limits the rule to apply only when the resource is in that role. Allowed values: Started, `Slave,` and `Master`. NOTE: A rule with `role="Master"` can not determine the initial location of a clone instance. It will only affect which of the active instances will be promoted.
`score`	The score to apply if the rule evaluates to `true`. Limited to use in rules that are part of location constraints.
`score-attribute`	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.
`boolean-op`	How to combine the result of multiple expression objects. Allowed values: and and `or`.

8.1. Node Attribute Expressions

Expression objects are used to control a resource based on the attributes defined by a node or nodes. In addition to any attributes added by the administrator, each node has a built-in node attribute called #uname that can also be used.

Table 8.2. Properties of an Expression

Field	Description
`value`	User supplied value for comparison
`attribute`	The node attribute to test
`type`	Determines how the value(s) should be tested. Allowed values: string, `integer`, `version`
`operation`	The comparison to perform. Allowed values: * lt - True if the node attribute’s value is less than `value` * gt - True if the node attribute’s value is greater than `value` * lte - True if the node attribute’s value is less than or equal to `value` * gte - True if the node attribute’s value is greater than or equal to `value` * eq - True if the node attribute’s value is equal to `value` * ne - True if the node attribute’s value is not equal to `value` * defined - True if the node has the named attribute * not_defined - True if the node does not have the named attribute