diff --git a/doc/Pacemaker_Explained/en-US/Ch-Rules.txt b/doc/Pacemaker_Explained/en-US/Ch-Rules.txt index 3b87fdfac0..dbd970b694 100644 --- a/doc/Pacemaker_Explained/en-US/Ch-Rules.txt +++ b/doc/Pacemaker_Explained/en-US/Ch-Rules.txt @@ -1,593 +1,600 @@ = Rules = //// We prefer [[ch-rules]], but older versions of asciidoc don't deal well with that construct for chapter headings //// anchor:ch-rules[Chapter 8, Rules] indexterm:[Resource,Constraint,Rule] 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. == Rule Properties == .Properties of a Rule [width="95%",cols="2m,1,5<",options="header",align="center"] |========================================================= |Field |Default |Description |role |+Started+ |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. indexterm:[role,Constraint Rule] indexterm:[Constraint,Rule,role] |score | |The score to apply if the rule evaluates to +true+. Limited to use in rules that are part of location constraints. indexterm:[score,Constraint Rule] indexterm:[Constraint,Rule,score] |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. indexterm:[score-attribute,Constraint Rule] indexterm:[Constraint,Rule,score-attribute] |boolean-op |+and+ |How to combine the result of multiple expression objects. Allowed values are +and+ and +or+. indexterm:[boolean-op,Constraint Rule] indexterm:[Constraint,Rule,boolean-op] |========================================================= == Node Attribute Expressions == indexterm:[Resource,Constraint,Attribute Expression] Expression objects are used to control a resource based on the attributes defined by a node or nodes. .Properties of an Expression [width="95%",cols="1m,1,5 ---- ==== .Equivalent expression ==== [source,XML] ---- ---- ==== .9am-5pm Monday-Friday ==== [source,XML] ------- ------- ==== Please note that the +16+ matches up to +16:59:59+, as the numeric value (hour) still matches! .9am-6pm Monday through Friday or anytime Saturday ==== [source,XML] ------- ------- ==== .9am-5pm or 9pm-12am Monday through Friday ==== [source,XML] ------- ------- ==== .Mondays in March 2005 ==== [source,XML] ------- ------- ==== [NOTE] ====== Because no time is specified with the above dates, 00:00:00 is implied. This means that the range includes all of 2005-03-01 but none of 2005-04-01. You may wish to write +end="2005-03-31T23:59:59"+ to avoid confusion. ====== .A full moon on Friday the 13th ===== [source,XML] ------- ------- ===== == Using Rules to Determine Resource Location == indexterm:[Rule,Determine Resource Location] indexterm:[Resource,Location,Determine by Rules] A location constraint may contain rules. When the constraint's outermost rule evaluates to +false+, the cluster treats the constraint as if it were not there. When the rule evaluates to +true+, the node's preference for running the resource is updated with the score associated with the rule. If this sounds familiar, it is because you have been using a simplified syntax for location constraint rules already. Consider the following location constraint: .Prevent myApacheRsc from running on c001n03 ===== [source,XML] ------- ------- ===== This constraint can be more verbosely written as: .Prevent myApacheRsc from running on c001n03 - expanded version ===== [source,XML] ------- ------- ===== The advantage of using the expanded form is that one can then add extra clauses to the rule, such as limiting the rule such that it only applies during certain times of the day or days of the week. === Location Rules Based on Other Node Properties === The expanded form allows us to match on node properties other than its name. If we rated each machine's CPU power such that the cluster had the following nodes section: .A sample nodes section for use with score-attribute ===== [source,XML] ------- ------- ===== then we could prevent resources from running on underpowered machines with this rule: [source,XML] ------- ------- === Using +score-attribute+ Instead of +score+ === When using +score-attribute+ instead of +score+, each node matched by the rule has its score adjusted differently, according to its value for the named node attribute. Thus, in the previous example, if a rule used +score-attribute="cpu_mips"+, +c001n01+ would have its preference to run the resource increased by +1234+ whereas +c001n02+ would have its preference increased by +5678+. == Using Rules to Control Resource Options == Often some cluster nodes will be different from their peers. Sometimes, these differences -- e.g. the location of a binary or the names of network interfaces -- require resources to be configured differently depending on the machine they're hosted on. By defining multiple +instance_attributes+ objects for the resource and adding a rule to each, we can easily handle these special cases. In the example below, +mySpecialRsc+ will use eth1 and port 9999 when run on +node1+, eth2 and port 8888 on +node2+ and default to eth0 and port 9999 for all other nodes. .Defining different resource options based on the node name ===== [source,XML] ------- ------- ===== The order in which +instance_attributes+ objects are evaluated is determined by their score (highest to lowest). If not supplied, score defaults to zero, and objects with an equal score are processed in listed order. If the +instance_attributes+ object has no rule or a +rule+ that evaluates to +true+, then for any parameter the resource does not yet have a value for, the resource will use the parameter values defined by the +instance_attributes+. For example, given the configuration above, if the resource is placed on node1: . +special-node1+ has the highest score (3) and so is evaluated first; its rule evaluates to +true+, so +interface+ is set to +eth1+. . +special-node2+ is evaluated next with score 2, but its rule evaluates to +false+, so it is ignored. . +defaults+ is evaluated last with score 1, and has no rule, so its values are examined; +interface+ is already defined, so the value here is not used, but +port+ is not yet defined, so +port+ is set to +9999+. == Using Rules to Control Cluster Options == indexterm:[Rule,Controlling Cluster Options] indexterm:[Cluster,Setting Options with Rules] Controlling cluster options is achieved in much the same manner as specifying different resource options on different nodes. The difference is that because they are cluster options, one cannot (or should not, because they won't work) use attribute-based expressions. The following example illustrates how to set a different +resource-stickiness+ value during and outside work hours. This allows resources to automatically move back to their most preferred hosts, but at a time that (in theory) does not interfere with business activities. .Change +resource-stickiness+ during working hours ===== [source,XML] ------- ------- ===== [[s-rules-recheck]] == Ensuring Time-Based Rules Take Effect == A Pacemaker cluster is an event-driven system. As such, it won't recalculate the best place for resources to run unless something (like a resource failure or configuration change) happens. This can mean that a location constraint that only allows resource X to run between 9am and 5pm is not enforced. If you rely on time-based rules, the +cluster-recheck-interval+ cluster option (which defaults to 15 minutes) is essential. This tells the cluster to periodically recalculate the ideal state of the cluster. For example, if you set +cluster-recheck-interval="5m"+, then sometime between 09:00 and 09:05 the cluster would notice that it needs to start resource X, and between 17:00 and 17:05 it would realize that X needed to be stopped. The timing of the actual start and stop actions depends on what other actions the cluster may need to perform first.