Capitolo 8. Regole

Indice

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.

Un'altra regola impostabile potrebbe essere quella di assegnare le macchine a differenti gruppi di processo (utilizzando gli attributi del nodo) basati sulle tempistiche ed utilizzare quindi questi attributi nella creazione delle constraint di tipo location.

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.

Tabella 8.1. Proprietà di una regola

Campo	Descrizione
`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. Espressioni relative agli attributi del nodo

Gli oggetti espressione sono utilizzati per controllare una risorsa basata sugli attributi definiti da uno o più nodi. In aggiunta a qualsiasi attributo aggiunto dall'amministratore, ogni nodo possiede un attributo predefinito che può essere utilizzato chiamato #uname.

Tabella 8.2. Proprietà di un'espressione

Campo	Descrizione
`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`	Il confronto da effettuare. Valori permessi: * 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