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Diffstat (limited to 'doc/sphinx/Pacemaker_Explained/constraints.rst')
| -rw-r--r-- | doc/sphinx/Pacemaker_Explained/constraints.rst | 65 |
1 files changed, 18 insertions, 47 deletions
diff --git a/doc/sphinx/Pacemaker_Explained/constraints.rst b/doc/sphinx/Pacemaker_Explained/constraints.rst index ab34c9f..a78d6c2 100644 --- a/doc/sphinx/Pacemaker_Explained/constraints.rst +++ b/doc/sphinx/Pacemaker_Explained/constraints.rst @@ -7,49 +7,6 @@ Resource Constraints -------------------- -.. index:: - single: resource; score - single: node; score - -Scores -###### - -Scores of all kinds are integral to how the cluster works. -Practically everything from moving a resource to deciding which -resource to stop in a degraded cluster is achieved by manipulating -scores in some way. - -Scores are calculated per resource and node. Any node with a -negative score for a resource can't run that resource. The cluster -places a resource on the node with the highest score for it. - -Infinity Math -_____________ - -Pacemaker implements **INFINITY** (or equivalently, **+INFINITY**) internally as a -score of 1,000,000. Addition and subtraction with it follow these three basic -rules: - -* Any value + **INFINITY** = **INFINITY** - -* Any value - **INFINITY** = -**INFINITY** - -* **INFINITY** - **INFINITY** = **-INFINITY** - -.. note:: - - What if you want to use a score higher than 1,000,000? Typically this possibility - arises when someone wants to base the score on some external metric that might - go above 1,000,000. - - The short answer is you can't. - - The long answer is it is sometimes possible work around this limitation - creatively. You may be able to set the score to some computed value based on - the external metric rather than use the metric directly. For nodes, you can - store the metric as a node attribute, and query the attribute when computing - the score (possibly as part of a custom resource agent). - .. _location-constraint: .. index:: @@ -434,6 +391,20 @@ Because the above example lets ``symmetrical`` default to TRUE, **Webserver** must be stopped before **Database** can be stopped, and **Webserver** should be stopped before **IP** if they both need to be stopped. +Symmetric and asymmetric ordering +_________________________________ + +A mandatory symmetric ordering of "start A then start B" implies not only that +the start actions must be ordered, but that B is not allowed to be active +unless A is active. For example, if the ordering is added to the configuration +when A is stopped (due to target-role, failure, etc.) and B is already active, +then B will be stopped. + +By contrast, asymmetric ordering of "start A then start B" means the stops can +occur in either order, which implies that B *can* remain active in the same +situation. + + .. index:: single: colocation single: constraint; colocation @@ -535,8 +506,8 @@ _____________________ | | | If ``rsc`` and ``with-rsc`` are specified, and ``rsc`` | | | | is a :ref:`promotable clone <s-resource-promotable>`, | | | | the constraint applies only to ``rsc`` instances in | - | | | this role. Allowed values: ``Started``, ``Promoted``, | - | | | ``Unpromoted``. For details, see | + | | | this role. Allowed values: ``Started``, ``Stopped``, | + | | | ``Promoted``, ``Unpromoted``. For details, see | | | | :ref:`promotable-clone-constraints`. | +----------------+----------------+--------------------------------------------------------+ | with-rsc-role | Started | .. index:: | @@ -548,8 +519,8 @@ _____________________ | | | ``with-rsc`` is a | | | | :ref:`promotable clone <s-resource-promotable>`, the | | | | constraint applies only to ``with-rsc`` instances in | - | | | this role. Allowed values: ``Started``, ``Promoted``, | - | | | ``Unpromoted``. For details, see | + | | | this role. Allowed values: ``Started``, ``Stopped``, | + | | | ``Promoted``, ``Unpromoted``. For details, see | | | | :ref:`promotable-clone-constraints`. | +----------------+----------------+--------------------------------------------------------+ | influence | value of | .. index:: | |