How to define a ConnectsTo relationship between service catalogs

This example shows how to define a relationship for NodeA (a SOURCE node) to connect to NodeB (a TARGET node) as in Figure 1.

  • We will define capabilities on the NodeB containing all information for NodeA to setup a connection.

  • We will define the relationship interfaces to setup the connection.

Steps

Step 1. Define an endpoint capability in the TARGET node (NodeB)

An endpoint capability contains information of a TARGET node for a SOURCE node to setup the connection.

In NodeB, we define the following capabilities block:

node_types:
  otc.nodes.SoftwareComponent.NodeB:
    ...
    capabilities:
      db_endpoint:
        type: tosca.capabilities.Endpoint.Database

In this example, we defined a new capability db_endpoint from the TOSCA type tosca.capabilities.Endpoint.Database. The capability db_endpoint will inherit all default properties from the TOSCA type (e.g., port, protocol, url_path).

In the designer, users can specifiy values for the capability db_endpoint. For example, they may set the port to 27017.

Tip

The tosca.capabilities.Endpoint also has a runtime attribute ip_address. The orchestrator will automatically set the IP address of the hosted compute node to this attribute. A SOURCE node can use this runtime attribute to setup a connection.

Step 2. Define a requirement in the SOURCE node (NodeA)

In the NodeA node, add the following requirements block:

node_types:
  otc.nodes.NodeA:
    derived_from: tosca.nodes.WebApplication
    ...
    requirements:
      - db_endpoint:
          # NodeA requires a node that has the capability Endpoint.Database
          capability: tosca.capabilities.Endpoint.Database
          # NodeA uses this relationship to setup the connection (see step 3)
          relationship: otc.relationships.NodeAConnectToNodeB
          # (Optional) specifiy relationship instance one-to-one
          # it means, one NodeA has one NodeB
          occurrences: [1, 1]

Step 3: Define the relationship

Define a new relationship otc.relationships.NodeAConnectToNodeB, how NodeA setups the connection with NodeB:

relationship_types:
  otc.relationships.NodeAConnectToNodeB:
    derived_from: tosca.relationships.ConnectsTo
    interfaces:
      Configure:
        pre_configure_source:
          inputs:
            # The input NODEA_PORT gets the port property of NodeA
            NODEA_PORT: { get_property: [SOURCE, port] }
            # The input NODEB_PORT gets the port property of NodeB
            NODEB_PORT: { get_property: [TARGET, port] }
            # The input NODEB_IP gets the runtime attribute ip_address of NodeB
            NODEB_IP: { get_attribute: [TARGET, db_endpoint, ip_address] }
          implementation: scripts/setup-connection.sh

In the above example, we defined the interface pre_configure_source by providing a shell script (e.g., setup-connection.sh). The script uses the input parameters NODEA_PORT, NODEB_PORT, and NODEB_IP to configure NodeA to connect to NodeB.

Note

  • Use the function get_property to get a SOURCE or TARGET node property.

  • Use the function get_attribute to get a runtime attribute of a SOURCE or TARGET node (e.g., ip_address).

2. Relationship interfaces

In addition to the interface pre_configure_source, we have the following interfaces

../_images/relationship_lifecycle.png

Figure 2. Relationship lifecycle

2.1. Interfaces executed on the TARGET node

  • pre_configure_target: executes after the TARGET node is created.

  • post_configure_target: executes after the TARGET node is configured.

  • add_source: executes on TARGET node, notifying that the SOURCE node is up and running.

2.2. Interfaces executed on the SOURCE node

  • pre_configure_source executes after the SOURCE node is created.

  • post_configure_source: executes after the SOURCE node is configured.

  • add_target: executes after the SOURCE node is started.

  • remove_target: executes after the TARGET node is removed.

Note

  • The TARGET node is always up and running first before the SOURCE node.

  • All runtime attributes of the SOURCE node are not available until it is up and running (i.e., they are available in the add_source interface). Therefore, to configure the TARGET node with any runtime attributes of the SOURCE node, you can use the add_source interface.

last updated: 2025-10-17 08:12 UTC - commit: fa7a4dbee78af34f08573e27ab24203bb7680c70