Cluster Membership

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Cluster Membership

Cluster Membership¶

Concept¶

A Node can belong to at most one Cluster at any time. A node is referred to as an orphan node when it doesn’t belong to any cluster.

A node can be made a member of cluster when creation, or you can change the cluster membership after the cluster and and the node have been created.

Listing Nodes in a Cluster¶

Using the command cluster-node-list, you can list the nodes that are members of a specific cluster. For example, to list nodes in cluster c3, you can use the following command:

$ senlin cluster-node-list c3
+----------+--------+-------+--------+-------------+---------------------+
| id       | name   | index | status | physical_id | created_at          |
+----------+--------+-------+--------+-------------+---------------------+
| b28692a5 | stack1 | 1     | ACTIVE | fdf028a6    | 2015-07-07T05:23:40 |
| 4be10a88 | stack2 | 2     | ACTIVE | 7c87f545    | 2015-07-07T05:27:54 |
+----------+--------+-------+--------+-------------+---------------------+

You can use the name, the ID or the “short ID” of a cluster as the argument for node listing. If the specified cluster identifier cannot match any cluster or it matches more than one cluster, you will get an error message.

From the list, you can see the index, status, physical_id of each node in this cluster. Note that the id field and the physical_id field are shown as “short ID”s by default. If you want to see the full IDs, you can specify the --full-id (or -F) option to indicate that:

$ senlin cluster-node-list -F c3
+------------...-+--------+-------+--------+-------------+-----------..-+
| id             | name   | index | status | physical_id | created_at   |
+------------...-+--------+-------+--------+-------------+-----------..-+
| b28692a5-25... | stack1 | -1    | ACTIVE | fdf0...     | 2015-07-07.. |
| 4be10a88-e3... | stack2 | -1    | ACTIVE | 7c87...     | 2015-07-07.. |
+------------...-+--------+-------+--------+-------------+-----------..-+

In cases where you want to list nodes that have been soft-deleted, you can add the option --show-deleted (or -D) for this purpose. For example, the following command will list all nodes that were members of the webservers cluster, no matter the nodes are soft-deleted or not:

$ senlin cluster-node-list -D webservers

If the cluster size is very large, you may want to list the nodes in pages. This can be achieved by using the --marker (or -m) option together with the --limit (or -l) option. The marker option value specifies a node ID after which you want the resulted list to start; and the limit option value specifies the number of nodes you want to include in the resulted list. For example, the following command lists the nodes starting behind a specific node ID with the length of the list set to 10:

$ senlin cluster-node-list -m b28692a5 -l 10 webservers

Another useful option for listing nodes is the --filters (or -f) option. The option value accepts a string of format “K1=V1;K2=V2...”, where “K1” and “K2” are node properties for checking, “V1” and “V2” are values for filtering. The acceptable properties for filtering are name and status. For example, the following command lists cluster nodes from a cluster based on whether a node’s status is “ACTIVE”:

$ senlin cluster-node-list -f status=ACTIVE webservers

Specify the Cluster When Creating a Node¶

There are several ways to make a node a member of a cluster. When creating a node using command node-create, you can specify the option --cluster (or -c) to tell Senlin to which cluster the new node belongs. Please refer to Nodes for detailed instructions.

Adding Node(s) to A Cluster¶

When you already have some nodes and some clusters, you can add some specified nodes to a specified cluster using the command cluster-node-add. For example, the following command adds two nodes to a cluster:

$ senlin cluster-node-add -n node3,node4 cluster1

You can use the name, the ID or the “short ID” to name the node(s) to be added, you can also use the name, the ID or the “short ID” to specify the cluster. When the identifiers you specify cannot match any existing nodes or clusters respectively, you will receive an error message. If the identifier provided matches more than one object, you will get an error message as well.

Before Senlin engine performs the cluster membership changes, it will verify if the nodes to be added have the same profile type with the target cluster. If the profile types don’t match, you will get an error message.

When nodes are added to a cluster, they will get new index property values that can be used to uniquely identify them within the cluster.

Removing Node(s) from a Cluster¶

The senlin command line also provides command cluster-node-del to remove node(s) from a cluster. In this case, you can use the name, the ID or the “short ID” to specify the node(s) and the cluster. The identifier specified must uniquely identifies a node or a cluster object, or else you will get an error message indicating that the request was rejected. The following command removes two nodes from a cluster:

$ senlin cluster-node-del -n node21,node22 webservers

When performing this operation, Senlin engine will check if the specified nodes are actually members of the specified cluster. If any node from the specified node list does not belong to the target cluster, you will get an error message and the command fails.

When nodes are removed from a cluster, they will get their index property reset to -1.