红帽全球峰会第 18 章 Creating cluster resources that are active on multiple nodes (cloned resources)
You can clone a cluster resource so that the resource can be active on multiple nodes. For example, you can use cloned resources to configure multiple instances of an IP resource to distribute throughout a cluster for node balancing. You can clone any resource provided the resource agent supports it. A clone consists of one resource or one resource group.
Only resources that can be active on multiple nodes at the same time are suitable for cloning. For example, a Filesystem resource mounting a non-clustered file system such as ext4 from a shared memory device should not be cloned. Since the ext4 partition is not cluster aware, this file system is not suitable for read/write operations occurring from multiple nodes at the same time.
18.1. Creating and removing a cloned resource
You can create a resource and a clone of that resource at the same time. Create a resource and clone of the resource with the following single command.
pcs resource create resource_id [standard:[provider:]]type [resource options] [meta resource meta options] clone [clone_id] [clone options]You can create a clone of a previously-created resource or resource group with the following command.
pcs resource clone resource_id | group_id [clone_id][clone options]...
By default, the name of the clone will be resource_id-clone. You can set a custom name for the clone by specifying a value for the clone_id option.
You cannot create a resource group and a clone of that resource group in a single command.
When you create a resource or resource group clone that will be ordered after another clone, you should almost always set the interleave=true option. This ensures that copies of the dependent clone can stop or start when the clone it depends on has stopped or started on the same node. If you do not set this option, if a cloned resource B depends on a cloned resource A and a node leaves the cluster, when the node returns to the cluster and resource A starts on that node, then all of the copies of resource B on all of the nodes will restart. This is because when a dependent cloned resource does not have the interleave option set, all instances of that resource depend on any running instance of the resource it depends on.
Use the following command to remove a clone of a resource or a resource group. This does not remove the resource or resource group itself.
pcs resource unclone resource_id | clone_id | group_nameThe following table describes the options you can specify for a cloned resource.
| Field | Description |
|---|---|
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| Options inherited from resource that is being cloned, as described in the "Resource Meta Options" table in Configuring resource meta options. |
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| How many copies of the resource to start. Defaults to the number of nodes in the cluster. |
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How many copies of the resource can be started on a single node; the default value is |
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When stopping or starting a copy of the clone, tell all the other copies beforehand and when the action was successful. Allowed values: |
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Does each copy of the clone perform a different function? Allowed values:
If the value of this option is
If the value of this option is |
|
|
Should the copies be started in series (instead of in parallel). Allowed values: |
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Changes the behavior of ordering constraints (between clones) so that copies of the first clone can start or stop as soon as the copy on the same node of the second clone has started or stopped (rather than waiting until every instance of the second clone has started or stopped). Allowed values: |
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If a value is specified, any clones which are ordered after this clone will not be able to start until the specified number of instances of the original clone are running, even if the |
To achieve a stable allocation pattern, clones are slightly sticky by default, which indicates that they have a slight preference for staying on the node where they are running. If no value for resource-stickiness is provided, the clone will use a value of 1. Being a small value, it causes minimal disturbance to the score calculations of other resources but is enough to prevent Pacemaker from needlessly moving copies around the cluster. For information about setting the resource-stickiness resource meta-option, see Configuring resource meta options.
The following procedure creates and removes a resource clone.
Procedure
On one node of the cluster, create the resource clone.
When you create a clone of a resource, by default the clone takes on the name of the resource with
-cloneappended to the name. The following command creates a resource of typeapachenamedwebfarmand a clone of that resource namedwebfarm-clone.# pcs resource create webfarm apache cloneRemove the clone of a resource or a resource group. This does not remove the resource or resource group itself.
# pcs resource unclone webfarm
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