A node is a logical entity managed by the Senlin service. Each node can belong to at most one cluster. A node that does not belong to any cluster can be referred to as an “orphan” node.

Node Properties

There are some common properties that are defined for all nodes. The following properties are always available on a node:

  • profile_id: ID of the profile from which the node is created.
  • cluster_id: When a node is a member of a cluster, the cluster_id value indicates the ID of the owning cluster. For an orphan node, this property is empty.
  • name: The name of a node doesn’t have to be unique even in the scope of the owning cluster (if there is one). For nodes created by Senlin service upon policy enforcement or when performing certain actions, Senlin engine will generate names for them automatically.
  • index: Each node has an index value which is unique in the scope of its owning cluster. The value is used to uniquely identify the node inside a cluster. For orphan nodes, the index value will be -1.
  • role: Each node in a cluster may have a role to play. The value of this property is a string that specifies the role a node plays in the owning cluster. Each profile type may support different set of roles.
  • user: ID of the user who is the creator (owner) of the node.
  • project: ID of the Keystone project in which the node was created.
  • domain: ID of the Keystone domain in which the node was created.
  • init_at: The timestamp when the node object was initialized.
  • created_at: The timestamp when the node was created.
  • updated_at: The timestamp when last time the node was updated.
  • metadata: A list of key-value pairs that are associated with the node.
  • physical_id: The UUID of the physical object that backs this node. The property value is empty if there are no physical objects associated with it.
  • status: A string indicating the current status of the node.
  • status_reason: A string describing the reason why the node transited to its current status.
  • dependents: A dict contains dependency information between nova server/ heat stack node and container node. The container node’s id will be stored in ‘dependents’ property of its host node.

In addition to the above properties, when a node is retrieved and shown to the user, Senlin provides a pseudo-property named profile_name for user’s convenience.

Cluster Membership

A prerequisite for a node to become a member of a cluster is that the node must share the same profile type with the cluster. When adding nodes to an existing cluster, Senlin engine will check if the profile types actually match.

It is NOT treated as an error that a node has a different profile (identified by the profile object’s ID) from the cluster. The profile referenced by the cluster can be interpreted as the ‘desired’ profile, while the profile referenced by individual nodes can be treated as the ‘actual’ profile(s). When the cluster scales out, new nodes will use the ‘desired’ profile referenced by the cluster. When existing nodes are added to an existing cluster, the existing nodes may have different profile IDs from the cluster. In this case, Senlin will not force an unnecessary profile update to the nodes.

Creating A Node

When receiving a request to create a node, Senlin API checks if any required fields are missing and whether there are invalid values specified to some fields. The following fields are required for a node creation request:

  • name: Name of the node to be created;
  • profile_id: ID of the profile to be used for creating the backend physical object.

Optionally, the request can contain the following fields:

  • cluster_id: When specified, the newly created node will become a member of the specified cluster. Otherwise, the new node will be an orphan node. The cluster_id provided can be a name of a cluster, the UUID of a cluster or the short ID of a cluster.
  • role: A string value specifying the role the node will play inside the cluster.
  • metadata: A list of key-value pairs to be associated with the node.

Listing Nodes

Nodes in the current project can be queried/listed using some query parameters. None of these parameters is required. By default, the Senlin API will return all nodes that are not deleted.

When listing nodes, the following query parameters can be specified, individually or combined:

  • filters: a map containing key-value pairs that will be used for matching node records. Records that fail to match this criteria will be filtered out. The following strings are valid as filter keys:
    • name: name of nodes to list, can be a string or a list of strings;
    • status: status of nodes, can be a string or a list of strings;
  • cluster_id: A string specifying the name, the UUID or the short ID of a cluster for which the nodes are to be listed.
  • limit: a number that restricts the maximum number of records to be returned from the query. It is useful for displaying the records in pages where the page size can be specified as the limit.
  • marker: A string that represents the last seen UUID of nodes in previous queries. This query will only return results appearing after the specified UUID. This is useful for displaying records in pages.
  • sort: A string to enforce sorting of the results. It accepts a list of known property names of a node as sorting keys separated by commas. Each sorting key can optionally have either :asc or :desc appended to the key for controlling the sorting direction.
  • show_nested: A boolean indicating whether nested clusters should be included in the results. The default is True. This feature is yet to be supported.
  • global_project: A boolean indicating whether node listing should be done in a tenant safe way. When this value is specified as False (the default), only nodes from the current project that match the other criteria will be returned. When this value is specified as True, nodes that matching all other criteria would be returned, no matter in which project the node was created. Only a user with admin privilege is permitted to do a global listing.

Getting a Node

When a user wants to check the details about a specific node, he or she can specify one of the following values for query:

  • Node UUID: Query is performed strictly based on the UUID value given. This is the most precise query supported.
  • Node name: Senlin allows multiple nodes to have the same name. It is user’s responsibility to avoid name conflicts if needed. The output is the details of a node if the node name is unique, otherwise Senlin will return a message telling users that multiple nodes found matching this name.
  • short ID: Considering that UUID is a long string not so convenient to input, Senlin supports a short version of UUIDs for query. Senlin engine will use the provided string as a prefix to attempt a matching in the database. When the “ID” is long enough to be unique, the details of the matching node is returned, or else Senlin will return an error message indicating that multiple nodes were found matching the specified short ID.

Senlin engine service will try the above three ways in order to find a match in database.

In addition to the key for query, a user can provide an extra boolean option named show_details. When this option is set, Senlin service will retrieve the properties about the physical object that backs the node. For example, for a Nova server, this information will contain the IP address allocated to the server, along with other useful information.

In the returned result, Senlin injects the name of the profile used by the node for the user’s convenience.

Updating a Node

Some node properties are updatable after the node has been created. These properties include:

  • name: Name of node as seen by the user;
  • role: The role that is played by the node in its owning cluster;
  • metadata: The key-value pairs attached to the node;
  • profile_id: The ID of the profile used by the node.

Note that update of profile_id is different from the update of other properties in that it may take time to complete. When receiving a request to update the profile used by a node, the Senlin engine creates an Action that is executed asynchronously by a worker thread.

When validating the node update request, Senlin rejects requests that attempt to change the profile type used by the node.

Deleting a Node

A node can be deleted no matter if it is a member of a cluster or not. Node deletion is handled asynchronously in Senlin. When the Senlin engine receives a request, it will create an Action to be executed by a worker thread.

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