6.2. Order Constraints
Order constraints determine the order in which the resources run. You can configure an order constraint to determine the order in which resources start and stop.
Use the following command to configure an order constraint.
pcs constraint order [action] resource_id then [action] resource_id [options]
Table 6.2, “Properties of an Order Constraint”. summarizes the properties and options for configuring order constraints.
| Field | Description |
|---|---|
|
resource_id
|
The name of a resource on which an action is performed.
|
|
action
|
The action to perform on a resource. Possible values of the action property are as follows:
*
start - Start the resource.
*
stop - Stop the resource.
*
promote - Promote the resource from a slave resource to a master resource.
*
demote - Demote the resource from a master resource to a slave resource.
If no action is specified, the default action is
start. For information on master and slave resources, see Section 8.2, “Multi-State Resources: Resources That Have Multiple Modes”.
|
kind option
|
How to enforce the constraint. The possible values of the
kind option are as follows:
*
Optional - Only applies if both resources are starting and/or stopping. For information on optional ordering, see Section 6.2.2, “Advisory Ordering”.
*
Mandatory - Always (default value). If the first resource you specified is stopping or cannot be started, the second resource you specified must be stopped. For information on mandatory ordering, see Section 6.2.1, “Mandatory Ordering”.
*
Serialize - Ensure that no two stop/start actions occur concurrently for a set of resources.
|
symmetrical options
|
6.2.1. Mandatory Ordering
A mandatory constraints indicates that the second resource you specify cannot run without the first resource you specify being active. This is the default value of the
kind option. Leaving the default value ensures that the second resource you specify will react when the first resource you specify changes state.
- If the first resource you specified resource was running and is stopped, the second resource you specified will also be stopped (if it is running).
- If the first resource you specified resource was not running and cannot be started, the second resource you specified will be stopped (if it is running).
- If the first resource you specified is (re)started while the second resource you specified is running, the second resource you specified will be stopped and restarted.
