Cluster-Policy Bindings¶
Concept¶
A Policy object can attached to at least one Cluster at the same time. A cluster at any time can have more than one Policy objects attached to it.
After a policy object is attached to a cluster, you can still enable or disable it or update some properties of the policy object.
Listing Policies Attached to a Cluster¶
The senlin tool provides the cluster-policy-list command to list policy objects that are attached to a cluster. You can provide the name, the ID or the “short ID” of a cluster as the identifier to reference a cluster. For example, the command below lists the policies attached to the cluster webservers:
$ senlin cluster-policy-list webservers
Sorting the List¶
You can specify the sorting keys and sorting direction when list cluster policies, using the option --sort (or -o). The --sort option accepts a string of format key1[:dir1],key2[:dir2],key3[:dir3], where the keys used are properties of the policy bound to a cluster and the dirs can be one of asc and desc. When omitted, Senlin sorts a given key using asc as the default direction.
For example, the following command instructs the senlin command line to sort policy bindings using the enabled property in descending order:
$ senlin cluster-policy-list -o enabled:desc
When sorting the list of policies, enabled is the only key you can specify for sorting.
Filtering the List¶
The senlin command line also provides options for filtering the policy list at the server side. The option --filters (or -f) can be used for this purpose. For example, the following command filters clusters by the enabled field:
$ senlin cluster-policy-list -f enabled=True c3
+-----------+--------+-----------------------+---------+
| policy_id | policy | type | enabled |
+-----------+--------+-----------------------+---------+
| 0705f0f4 | up01 | senlin.policy.scaling | True |
+-----------+--------+-----------------------+---------+
The option --filters accepts a list of key-value pairs separated by semicolon (;), where each key-value pair is expected to be of format <key>=<value>. The only key that can be used for filtering as of today is enabled.
Attaching a Policy to a Cluster¶
Senlin permits policy objects to be attached to clusters and to be detached from clusters dynamically. When attaching a policy object to a cluster, you can customize the policy properties for the particular cluster. For example, you can specify whether the policy should be enabled once attached.
The following options are supported for the cluster-policy-attach command:
- --enabled (or -e): a boolean indicating whether the policy to be enabled once attached.
For example, the following command attaches a policy named up01 to the cluster c3, with its enabled status set to True:
$ senlin cluster-policy-attach -e -p up01 c3
Note that most of the time, Senlin doesn’t more than one policy of the same type to be attached to the same cluster. This restriction is relaxed for some policy types. For example, when working with policies about scaling, you can actually attach more than one policy instances to the same cluster, each of which is about a specific scenario.
For the identifiers specified for the cluster and the policy, you can use the name, the ID or the “short ID” of an object. The Senlin engine will try make a guess on each case. If no entity matches the specified identifier or there are more than one entity matching the identifier, you will get an error message.
Showing Policy Properties on a Cluster¶
To examine the detailed properties of a policy object that has been attached to a cluster, you can use the command cluster-policy-show with the policy identifier and the cluster identifier specified. For example:
$ senlin cluster-policy-show -p dp01 c3
+--------------+--------------------------------------+
| Property | Value |
+--------------+--------------------------------------+
| cluster_id | 2b7e9294-b5cd-470f-b191-b18f7e672495 |
| cluster_name | c3 |
| enabled | True |
| policy | dp01 |
| policy_id | 239d7212-6196-4a89-9446-44d28717d7de |
| type | senlin.policy.deletion-1.0 |
+--------------+--------------------------------------+
You can use the name, the ID or the “short ID” of a policy and/or a cluster to name the objects.
Updating Policy Properties on a Cluster¶
Once a policy is attached to a cluster, you can request its property on this cluster be changed by using the command cluster-policy-update. At this stage, you can specify the enabled property to be updated.
For example, the following command disables a policy on the specified cluster:
$ senlin cluster-policy-update -e False -p dp01 mycluster
The Senlin engine will perform validation of the arguments in the same way as that for the policy attach operation. You can use the name, the ID or the “short ID” of an entity to reference it, as you do with the policy attach operation as well.
Detach a Policy from a Cluster¶
Finally, to remove the binding between a specified policy object from a cluster, you can use the cluster-policy-detach command as shown below:
$ senlin cluster-policy-detach -p dp01 mycluster
This command will detach the specified policy from the specified cluster. You will use the option --policy (or -p) to specify the policy.
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