Reusing Parts of the Configuration ---------------------------------- Pacemaker provides multiple ways to simplify the configuration XML by reusing parts of it in multiple places. Besides simplifying the XML, this also allows you to manipulate multiple configuration elements with a single reference. Reusing Resource Definitions ############################ If you want to create lots of resources with similar configurations, defining a *resource template* simplifies the task. Once defined, it can be referenced in primitives or in certain types of constraints. Configuring Resources with Templates ____________________________________ The primitives referencing the template will inherit all meta-attributes, instance attributes, utilization attributes and operations defined in the template. And you can define specific attributes and operations for any of the primitives. If any of these are defined in both the template and the primitive, the values defined in the primitive will take precedence over the ones defined in the template. Hence, resource templates help to reduce the amount of configuration work. If any changes are needed, they can be done to the template definition and will take effect globally in all resource definitions referencing that template. Resource templates have a syntax similar to that of primitives. .. topic:: Resource template for a migratable Xen virtual machine .. code-block:: xml Once you define a resource template, you can use it in primitives by specifying the ``template`` property. .. topic:: Xen primitive resource using a resource template .. code-block:: xml In the example above, the new primitive ``vm1`` will inherit everything from ``vm-template``. For example, the equivalent of the above two examples would be: .. topic:: Equivalent Xen primitive resource not using a resource template .. code-block:: xml If you want to overwrite some attributes or operations, add them to the particular primitive's definition. .. topic:: Xen resource overriding template values .. code-block:: xml In the example above, the new primitive ``vm2`` has special attribute values. Its ``monitor`` operation has a longer ``timeout`` and ``interval``, and the primitive has an additional ``stop`` operation. To see the resulting definition of a resource, run: .. code-block:: none # crm_resource --query-xml --resource vm2 To see the raw definition of a resource in the CIB, run: .. code-block:: none # crm_resource --query-xml-raw --resource vm2 Using Templates in Constraints ______________________________ A resource template can be referenced in the following types of constraints: - ``order`` constraints (see :ref:`s-resource-ordering`) - ``colocation`` constraints (see :ref:`s-resource-colocation`) - ``rsc_ticket`` constraints (for multi-site clusters as described in :ref:`ticket-constraints`) Resource templates referenced in constraints stand for all primitives which are derived from that template. This means, the constraint applies to all primitive resources referencing the resource template. Referencing resource templates in constraints is an alternative to resource sets and can simplify the cluster configuration considerably. For example, given the example templates earlier in this chapter: .. code-block:: xml would colocate all VMs with ``base-rsc`` and is the equivalent of the following constraint configuration: .. code-block:: xml .. note:: In a colocation constraint, only one template may be referenced from either ``rsc`` or ``with-rsc``; the other reference must be a regular resource. Using Templates in Resource Sets ________________________________ Resource templates can also be referenced in resource sets. For example, given the example templates earlier in this section, then: .. code-block:: xml is the equivalent of the following constraint using a sequential resource set: .. code-block:: xml Or, if the resources referencing the template can run in parallel, then: .. code-block:: xml is the equivalent of the following constraint configuration: .. code-block:: xml .. _s-reusing-config-elements: Reusing Rules, Options and Sets of Operations ############################################# Sometimes a number of constraints need to use the same set of rules, and resources need to set the same options and parameters. To simplify this situation, you can refer to an existing object using an ``id-ref`` instead of an ``id``. So if for one resource you have .. code-block:: xml Then instead of duplicating the rule for all your other resources, you can instead specify: .. topic:: **Referencing rules from other constraints** .. code-block:: xml .. important:: The cluster will insist that the ``rule`` exists somewhere. Attempting to add a reference to a non-existing rule will cause a validation failure, as will attempting to remove a ``rule`` that is referenced elsewhere. The same principle applies for ``meta_attributes`` and ``instance_attributes`` as illustrated in the example below: .. topic:: Referencing attributes, options, and operations from other resources .. code-block:: xml ``id-ref`` can similarly be used with ``resource_set`` (in any constraint type), ``nvpair``, and ``operations``. Tagging Configuration Elements ############################## Pacemaker allows you to *tag* any configuration element that has an XML ID. The main purpose of tagging is to support higher-level user interface tools; Pacemaker itself only uses tags within constraints. Therefore, what you can do with tags mostly depends on the tools you use. Configuring Tags ________________ A tag is simply a named list of XML IDs. .. topic:: Tag referencing three resources .. code-block:: xml What you can do with this new tag depends on what your higher-level tools support. For example, a tool might allow you to enable or disable all of the tagged resources at once, or show the status of just the tagged resources. A single configuration element can be listed in any number of tags. Using Tags in Constraints and Resource Sets ___________________________________________ Pacemaker itself only uses tags in constraints. If you supply a tag name instead of a resource name in any constraint, the constraint will apply to all resources listed in that tag. .. topic:: Constraint using a tag .. code-block:: xml In the example above, assuming the ``all-vms`` tag is defined as in the previous example, the constraint will behave the same as: .. topic:: Equivalent constraints without tags .. code-block:: xml A tag may be used directly in the constraint, or indirectly by being listed in a :ref:`resource set ` used in the constraint. When used in a resource set, an expanded tag will honor the set's ``sequential`` property. Filtering With Tags ___________________ The ``crm_mon`` tool can be used to display lots of information about the state of the cluster. On large or complicated clusters, this can include a lot of information, which makes it difficult to find the one thing you are interested in. The ``--resource=`` and ``--node=`` command line options can be used to filter results. In their most basic usage, these options take a single resource or node name. However, they can also be supplied with a tag name to display several objects at once. For instance, given the following CIB section: .. code-block:: xml The following would be output for ``crm_mon --resource=inactive-rscs -r``: .. code-block:: none Cluster Summary: * Stack: corosync * Current DC: cluster02 (version 2.0.4-1.e97f9675f.git.el7-e97f9675f) - partition with quorum * Last updated: Tue Oct 20 16:09:01 2020 * Last change: Tue May 5 12:04:36 2020 by hacluster via crmd on cluster01 * 5 nodes configured * 27 resource instances configured (4 DISABLED) Node List: * Online: [ cluster01 cluster02 ] Full List of Resources: * Clone Set: inactive-clone [inactive-dhcpd] (disabled): * Stopped (disabled): [ cluster01 cluster02 ] * Resource Group: inactive-group (disabled): * inactive-dummy-1 (ocf::pacemaker:Dummy): Stopped (disabled) * inactive-dummy-2 (ocf::pacemaker:Dummy): Stopped (disabled)