Relationships


relationships let you define how nodes relate to one another. For example, a web_server node can be contained_in a vm node or an application node can be connected_to a database node.

Declaration

  
node_templates:

  node:
    ...
    relationships:
      - type: ""
        target: ""
        properties:
            connection_type: ""
        source_interfaces: {}
        target_interfaces: {}
    ...
  

Schema

Keyname Required Type Description
type yes string Either a newly declared relationship type or one of the relationship types provided by default when importing the types.yaml file.
target yes string The node’s name to relate the current node to.
connection_type no string valid values: all_to_all and all_to_one (explained below)
source_interfaces no dict A dict of interfaces.
target_interfaces no dict A dict of interfaces.


By default, nodes can be related by using the relationship types described below. You may also declare your own relationship types.

The cloudify.relationships.depends_on relationship type

A node depends on another node. For example, the creation of a new subnet depends on the creation of a new network.

Note

The cloudify.relationships.depends_on relationship type is meant to be used as a logical representation of dependencies between nodes. As such, you should only use it in very specific cases when the other two do not fit or when you want to suggest that a certain node should be created before or after another for the sake of ordering.

The other two relationship types inherit from the cloudify.relationships.depends_on relationship type. The semantics of the cloudify.relationships.connected_to relationship type is the same, therefore, usage reference should be dictated by cloudify.relationships.connected_to which is described below.

The cloudify.relationships.contained_in relationship type

A node is contained in another node. For example, a web server is contained within a vm.

Example:

  
node_templates:

  vm:
    type: cloudify.nodes.Compute
    capabilities:
      scalable:
        properties:
          default_instances: 2

  http_web_server:
    type: cloudify.nodes.WebServer
    capabilities:
      scalable:
        properties:
          default_instances: 2
    properties:
      port: { get_input: webserver_port }
    relationships:
      - type: cloudify.relationships.contained_in
        target: vm
    interfaces:
      cloudify.interfaces.lifecycle:
        configure: scripts/configure.sh
        start:
          implementation: scripts/start.sh
          inputs:
            process:
              env:
                port: { get_input: webserver_port }
        stop: scripts/stop.sh
  

In the above example, the http_web_server node is contained within a vm node. Practically, this means that:

  • The vm’s node instances will be created before the http_web_server’s node instances.
  • Two instances of the http_web_server node will be created within each of the two node instances of the vm node. This means that we will have 4 node instances of the http_web_server node.

The last bullet is a bit tricky. The number of node instances for each node that is contained within another node will be determined by multiplying the number of instances requested for the contained node and the actual number of instances of the node it is contained in.

Let’s break this down:

node ‘A’ is set to have ‘X’ node instances; node ‘B’ is set to have ‘Y’ node instances; node B is cloudify.relationships.contained_in node A. Then, node ‘A’ will have X node instances and node ‘B’ will have X*Y node instances - Y node instances per node instance in ‘A’.

Note

There can only be one cloudify.relationships.contained_in relationship per node!

Note that the implementation of cloudify.relationships.contained_in doesn’t necessarily dictate that a node must be physically contained in another node.

For instance, a counter-example to the http_web_server in a vm would be an ip node that is contained in a network node. While the ip isn’t really contained within the network itself, if two instances of the ip node will be cloudify.relationships.contained_in the network node, you will have 2 ip node instances in each instance of the network node.

The cloudify.relationships.connected_to relationship type

A node is connected to another node. For example, an application is connected to a database and both of them are contained in a vm.

Example:

  
node_templates:

  application:
    type: web_app
    capabilities:
      scalable:
        properties:
          default_instances: 2
    relationships:
      - type: cloudify.relationships.contained_in
        target: vm
      - type: cloudify.relationships.connected_to
        target: database

  database:
    type: database
    capabilities:
      scalable:
        properties:
          default_instances: 1
    relationships:
      - type: cloudify.relationships.contained_in
        target: vm

  vm:
    type: cloudify.nodes.Compute
    capabilities:
      scalable:
        properties:
          default_instances: 2
  

In the above example, an application node is connected to a database node (and both the database and the application nodes are contained in a vm node.)

Note that since we deployed two vm node instances, two application node instances and one database node instance, each of the two vm’s will contain one database node instance and two application node instances as explained in the cloudify.relationships.contained_in relationship type.

This actually means that we will have four application node instances (two on each vm node instance) and two database node instance (one on each vm node instance). All application node instances will be connected to each of the two databases residing on the two vm’s.

Multi-instance cloudify.relationships.connected_to semantics

A specific feature in cloudify.relationships.connected_to allows you to connect a node to an arbitrary instance of another node.

Example:

  
node_templates:

  application:
    type: web_app
    capabilities:
      scalable:
        properties:
          default_instances: 2
    relationships:
      - type: cloudify.relationships.connected_to
        target: database
        properties:
            connection_type: all_to_one

  database:
    type: database
    capabilities:
      scalable:
        properties:
          default_instances: 2
  

In the above example we have two application node instances connecting to one of the two database node instances arbitrarily.

The default configuration for connection_type is all_to_all.

The same connection_type configuration can be applied to a cloudify.relationships.contained_in relationship type, though it will virtually have no effect.

connection_type: all_to_all and all_to_one

As mentioned previously, the relationship types cloudify.relationships.connected_to and cloudify.relationships.depends_on and those that derive from it have a property named connection_type whose value can be either all_to_all or all_to_one (The default value is all_to_all). The following diagrams aim to make their semantics clearer.

all_to_all

Consider this blueprint:

  
node_templates:
  application:
    type: web_app
    capabilities:
      scalable:
        properties:
          default_instances: 2
    relationships:
      - type: cloudify.relationships.connected_to
        target: database
        properties:
            connection_type: all_to_all
  database:
    type: database
    capabilities:
      scalable:
        properties:
          default_instances: 2
  

When deployed, we will have 2 node instances of the application node and 2 node instances of the database node. All application node instances will be connected to all database node instances.

For example, consider 2 Node.js application servers that need to connect to 2 memcached nodes.

all_to_all diagram

all_to_one

Consider this blueprint:

  
node_templates:
  application:
    type: web_app
    capabilities:
      scalable:
        properties:
          default_instances: 2
    relationships:
      - type: cloudify.relationships.connected_to
        target: database
        properties:
            connection_type: all_to_one
  database:
    type: database
    capabilities:
      scalable:
        properties:
          default_instances: 2
  

When deployed, we will have 2 node instances of the application node and 2 node instances of the database node. All application node instances will be connected to one database node instance (chosen at random).

For example, consider 2 Node.js application servers that need to add themselves as users on a single cassandra node.

all_to_one diagram

Relationship Instances

Let’s assume you have a node with two instances and two relationships configured for them.

When a deployment is created, node instances are instantiated in the model. Just like node instances are instantiated for each node, relationship instances are instantiated for each relationship.

Declaring Relationship Types

You can declare your own relationship types in the relationships section in the blueprint. This is useful when you want to change the default implementation of how nodes interact.

Relationship Type Declaration

Declaring relationship types is done like so:

  
relationships:

  relationship1:
    derived_from: ""
    source_interfaces: {}
    target_interfaces: {}
    properties:
      connection_type: ""

  relationship2: {}
    ...
  

Relationship Type Schema

Keyname Required Type Description
derived_from no string The relationship type from which the new relationship is derived.
source_interfaces no dict A dict of interfaces.
target_interfaces no dict A dict of interfaces.
connection_type no string valid values: all_to_all and all_to_one


Relationship Type Example

  
relationships:
  app_connected_to_db:
    derived_from: cloudify.relationships.connected_to
    source_interfaces:
      cloudify.interfaces.relationship_lifecycle:
        postconfigure:
          implementation: scripts/configure_my_connection.py

node_templates:
  application:
    type: web_app
    capabilities:
      scalable:
        properties:
          default_instances: 2
    relationships:
      - type: cloudify.relationships.contained_in
        target: vm
      - type: app_connected_to_db
        target: database
  

In the above example, we create a relationship type called app_connected_to_db which inherits from the base cloudify.relationships.connected_to relationship type and implements a specific configuration (by running scripts/configure_my_connection.py) for the type.

Relationship Interfaces

Each relationship type (and instance) has source_interfaces and target_interfaces.

For a given node:

  • source_interfaces defines interfaces of operations that will be executed on the node in which the relationship is declared.
  • target_interfaces defines interfaces of operations that will be executed on the node its relationship targets.

Note

Having the interfaces defined under source_interfaces and target_interfaces does not necessarily mean that their operations will be executed. That is, operations defined in cloudify.interfaces.relationship_lifecycle will be executed when running install/uninstall workflows. We can also add a custom relationship interface and write a custom workflow that will execute operations from the new interface.

Example:

  
relationships:
  source_connected_to_target:
    derived_from: cloudify.relationships.connected_to
    source_interfaces:
      cloudify.interfaces.relationship_lifecycle:
        postconfigure:
          implementation: scripts/configure_source_node.py
    target_interfaces:
      cloudify.interfaces.relationship_lifecycle:
        postconfigure:
          implementation: scripts/configure_target_node.py

node_templates:
  source_node:
    type: app
    relationships:
      - type: source_connected_to_target
        target: target_node
  

In the above example we can see that the postconfigure lifecycle operation in the source_connected_to_target relationship type is configured once in its source_interfaces section and target_interfaces section.

As such, the configure_source_node.py script will be executed on host instances of source_node and the configure_target_node.py will be executed on host instances of target_node (this is only true if the plugin executor is configured as host_agent and not central_deployment_agent. Otherwise, source_interfaces operations and target_interfaces operations are all executed on the manager.)

How Relationships Affect Node Creation

Declaring relationships affects the node creation/teardown flow in respect to the install/uninstall workflows respectively.

When declaring a relationship and using the built in install workflow, the first lifecycle operation of the source node will only be executed once the entire set of lifecycle operations of the target node were executed and completed. When using the uninstall workflow, the opposite will be true.

So, for instance, in the previous example, all source operations (node_instance operations, source_interfaces relationships operations and target_interfaces relationship operations) for source_node will be executed AFTER ALL target_node operations have been completed. This removes any uncertainties about whether a node was ready to have another node connect to or be contained in it due to it not being available. Of course, it’s up to the user to define what “ready” means.