Node Types

node_types are used for defining common properties and behaviors for Node Templates. node-templates can then be created based on these types, inheriting their definitions.

A partial definition (type only) is treated a requirement that the node template declares an artifact of that name and type.

Declaration

node_types:

 type1:
   derived_from: tosca.nodes.Root
   properties:
     ...
   interfaces:
     ...

 type2:
   ...
 ...

Definition

Keyname	Required	Type	Description
derived_from	yes	string or list	Parent type(s).
metadata	no	dictionary	A dictionary of node metadata.
properties	no	dictionary	A dictionary of node properties.
attributes	no	dictionary	A dictionary of node attributes.
capabilities	no	dictionary	A dictionary of node capabilities.
requirements	no	dictionary	A dictionary of node requirements.
artifacts	no	dictionary	A dictionary of artifact definitions.
interfaces	no	dictionary	A dictionary of node interfaces.

derived_from

The derived_from property may be used to build over and extend an existing type. This is useful for further extracting common properties and behaviors, this time in between types.

Using this mechanism, one can build various type hierarchies which can be reused over different application service templates.

As a TOSCA extension, Unfurl support multiple inheritance if a derived_from if a list of type names.

When a type derives from another type, its interfaces and properties keys get merged with the parent type’s interfaces and properties keys. The merge is on the property/operation level: A property defined on the parent type will be overridden by a property with the same name defined on the deriving type. The same is true for an interface operation mapping - however, it is important to note that it’s possible to add in the deriving type additional operation mappings to an interface defined in the parent type. See the examples section for more on this.

properties

The properties property may be used to define a common properties schema for node templates.

properties is a dictionary from a property name to a dictionary describing the property. The nested dictionary includes the following keys:

Keyname	Required	Type	Description
description	no	string	Description for the property.
type	no	string	Property type. Not specifying a data type means the type can be anything (including types not listed in the valid types). Valid types: string, integer, float, boolean or a :ref:` Custom Data Types <data_types>`.
default	no	<any>	An optional default value for the property.
required	no	boolean	Specifies whether the property is required.

artifacts

As a TOSCA extension, Unfurl let’s you define artifacts on node types in addition to node templates. If the artifact is partially defined (type only), then node templates will be required to declare an artifact of that name and type. If the artifact has a complete definition it will be treated as if it was declared on node templates that match this node type.

interfaces

The interfaces property may be used to define common behaviors for node templates.

Examples

node_types:
  nodecellar.nodes.MongoDatabase:
    derived_from: tosca.nodes.DBMS
    properties:
      port:
        description: MongoDB port
        type: integer
    interfaces:
      Standard:
        create: scripts/mongo/install-mongo.sh
        start: scripts/mongo/start-mongo.sh
        stop: scripts/mongo/stop-mongo.sh

An example of how to use this type follows:

node_templates:
  MongoDB1:
    type: nodecellar.nodes.MongoDatabase
  MongoDB2:
    type: nodecellar.nodes.MongoDatabase

Each of these two nodes will now have both the port property and the three operations defined for the nodecellar.nodes.MongoDatabase type.

Finally, an example on how to extend an existing type by deriving from it:

node_types:
  nodecellar.nodes.MongoDatabaseExtended:
    derived_from: nodecellar.nodes.MongoDatabase
    properties:
      enable_replication:
        description: MongoDB replication enabling flag
        type: boolean
        default: false
    interfaces:
      Standard:
        create: scripts/mongo/install-mongo-extended.sh
        configure: scripts/mongo/configure-mongo-extended.sh

The nodecellar.nodes.MongoDatabaseExtended type derives from the nodecellar.nodes.MongoDatabase type which was defined in the previous example; As such, it derives its properties and interfaces definitions, which get either merged or overridden by the ones it defines itself.

A node template whose type is nodecellar.nodes.MongoDatabaseExtended will therefore have both the port and enable_replication properties, as well as the following interfaces mapping:

interfaces:
  Standard:
    create: scripts/mongo/install-mongo-extended.sh
    configure: scripts/mongo/configure-mongo-extended.sh
    start: scripts/mongo/start-mongo.sh
    stop: scripts/mongo/stop-mongo.sh

As it is evident, the configure operation, which is mapped only in the extending type, got merged with the start and stop operations which are only mapped in the parent type, while the create operation, which is defined on both types, will be mapped to the value set in the extending type.