Chapter 17. Determining resource location with rules For more complicated location constraints, you can use Pacemaker rules to determine a resource's location. 17.1. Pacemaker rules Pacemaker rules can be used to make your configuration more dynamic. One 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 depends on the context in which the rule is being used. Table 17.1. 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" cannot 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 . The default value is and . 17.1.1. Node attribute expressions Node attribute expressions are used to control a resource based on the attributes defined by a node or nodes. Table 17.2. Properties of an Expression Field Description attribute The node attribute to test type Determines how the value(s) should be tested. Allowed values: string , integer , number (RHEL 8.4 and later), version . The default value is string . 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 value User supplied value for comparison (required unless operation is defined or not_defined ) In addition to any attributes added by the administrator, the cluster defines special, built-in node attributes for each node that can also be used, as described in the following table. Table 17.3. Built-in Node Attributes Name Description #uname Node name #id Node ID #kind Node type. Possible values are cluster , remote , and container . The value of kind is remote for Pacemaker Remote nodes created with the ocf:pacemaker:remote resource, and container for Pacemaker Remote guest nodes and bundle nodes. #is_dc true if this node is a Designated Controller (DC), false otherwise #cluster_name The value of the cluster-name cluster property, if set #site_name The value of the site-name node attribute, if set, otherwise identical to #cluster-name #role The role the relevant promotable clone has on this node. Valid only within a rule for a location constraint for a promotable clone. 17.1.2. Time/date based expressions Date expressions are used to control a resource or cluster option based on the current date/time. They can contain an optional date specification. Table 17.4. Properties of a Date Expression Field Description start A date/time conforming to the ISO8601 specification. end A date/time conforming to the ISO8601 specification. operation Compares the current date/time with the start or the end date or both the start and end date, depending on the context. Allowed values: * gt - True if the current date/time is after start * lt - True if the current date/time is before end * in_range - True if the current date/time is after start and before end * date-spec - performs a cron-like comparison to the current date/time 17.1.3. Date specifications Date specifications are used to create cron-like expressions relating to time. Each field can contain a single number or a single range. Instead of defaulting to zero, any field not supplied is ignored. For example, monthdays="1" matches the first day of every month and hours="09-17" matches the hours between 9 am and 5 pm (inclusive). However, you cannot specify weekdays="1,2" or weekdays="1-2,5-6" since they contain multiple ranges. Table 17.5. Properties of a Date Specification Field Description id A unique name for the date hours Allowed values: 0-23 monthdays Allowed values: 0-31 (depending on month and year) weekdays Allowed values: 1-7 (1=Monday, 7=Sunday) yeardays Allowed values: 1-366 (depending on the year) months Allowed values: 1-12 weeks Allowed values: 1-53 (depending on weekyear ) years Year according the Gregorian calendar weekyears May differ from Gregorian years; for example, 2005-001 Ordinal is also 2005-01-01 Gregorian is also 2004-W53-6 Weekly moon Allowed values: 0-7 (0 is new, 4 is full moon). 17.2. Configuring a Pacemaker location constraint using rules Use the following command to configure a Pacemaker constraint that uses rules. If score is omitted, it defaults to INFINITY. If resource-discovery is omitted, it defaults to always . For information about the resource-discovery option, see Limiting resource discovery to a subset of nodes . As with basic location constraints, you can use regular expressions for resources with these constraints as well. When using rules to configure location constraints, the value of score can be positive or negative, with a positive value indicating "prefers" and a negative value indicating "avoids". The expression option can be one of the following where duration_options and date_spec_options are: hours, monthdays, weekdays, yeardays, months, weeks, years, weekyears, and moon as described in the "Properties of a Date Specification" table in Date specifications . defined|not_defined attribute attribute lt|gt|lte|gte|eq|ne [string|integer|number (RHEL 8.4 and later) |version] value date gt|lt date date in_range date to date date in_range date to duration duration_options ... date-spec date_spec_options expression and|or expression ( expression ) Note that durations are an alternative way to specify an end for in_range operations by means of calculations. For example, you can specify a duration of 19 months. The following location constraint configures an expression that is true if now is any time in the year 2018. The following command configures an expression that is true from 9 am to 5 pm, Monday through Friday. Note that the hours value of 16 matches up to 16:59:59, as the numeric value (hour) still matches. The following command configures an expression that is true when there is a full moon on Friday the thirteenth. To remove a rule, use the following command. If the rule that you are removing is the last rule in its constraint, the constraint will be removed.

Commands:
pcs constraint location rsc rule [resource-discovery= option ] [role=master|slave] [score= score | score-attribute= attribute ] expression
pcs constraint location Webserver rule score=INFINITY date-spec years=2018
pcs constraint location Webserver rule score=INFINITY date-spec hours="9-16" weekdays="1-5"
pcs constraint location Webserver rule date-spec weekdays=5 monthdays=13 moon=4
pcs constraint rule remove rule_id