Relationships

relationships enable you to 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 name of the node to which the current node is related.
connection_type no string Valid values: all_to_all and all_to_one (See explanation below.)
source_interfaces no dict A dictionary of interfaces.
target_interfaces no dict A dictionary of interfaces.


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

The cloudify.relationships.depends_on Relationship Type

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

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:

To explain further:
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

You may only use one cloudify.relationships.contained_in relationship per node.

Note that the implementation of cloudify.relationships.contained_in does not 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 is an ip node that is contained in a network node. Although the IP isn’t actually contained within the network itself, if two instances of the ip node have the cloudify.relationships.contained_in relationship type with the network node, there will be two 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.)

Since there are two vm node instances, two application node instances and one database node instance deployed, each of the 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 there are four application node instances (two on each VM node instance) and two database node instances (one on each VM node instance). All application node instances are 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 there two application node instances that arbitrarily connect to one of the two database node instances.

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, although it has virtually no effect.

The cloudify.relationships.depends_on_lifecycle_operation Relationship Type

As an extension of cloudify.relationships.depends_on relationship type, when a node depends on another node but could start creation earlier in the lifecycle operations of that node (precreate, create, configure, start), this is relevant in case that the requirements of the node are met earlier in the creation process. For example application service node that uses a DB service which only needs it’s connection url, so when this url is available, probably after the create lifecycle operation, the application service node could start creation and to wait for the DB node to fully finish.

Notice, that a node could only depend on a defined lifecycle operation, due to that only an operation could generate outputs for it’s users.

Usage example:

node_templates:

  application:
    type: web_app
    capabilities:
      scalable:
        properties:
          default_instances: 2
    relationships:
      - type: cloudify.relationships.depends_on_lifecycle_operation
        target: database
        properties:
            operation: create

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

In a multi-service architecture application, the scenario of a shared resource (for example: shared DB service, filesystem, etc) is a common one. And in some cases there are dependencies to them by other application’s nodes, so in order to enforce those relationships is required or/and if a custom connection is needed (the custom connection will allow running a workflow on the shared resource, for example creating logs directory for each node in the deployment on a shared filesystem). The following relationships are for supporting these use cases.

The shared resource scenario is supported by the SharedResource node type, for further information please visit SharedResource.

The cloudify.relationships.depends_on_shared_resource Relationship Type

As an extension of cloudify.relationships.depends_on relationship type, this can only target a node of SharedResource type. This relationship will allow running any workflow (custom or not) ,which is defined in the target node’s deployment, as a part from establish and unlink relationship lifecycle operations. Also if the SharedResource node has been created with different Cloudify client connection, those settings will be taken from the node properties if exists else it will use default Cloudify client.

Relationship settings:

Simple example

node_templates:

  shared_resource_node:
    type: cloudify.nodes.SharedResource
    properties:
      resource_config:
        deployment:
            id: shared_resource_deployment

  app:
    type: cloudify.nodes.WebServer
    relationships:
      - type: cloudify.relationships.depends_on_shared_resource
        target: shared_resource_node
        target_interfaces:
          cloudify.interfaces.relationship_lifecycle:
            establish:
              inputs:
                workflow_id: custom_workflow
                parameters: {input: 'x'}
            unlink:
              inputs:
                workflow_id: un_custom_workflow
                timeout: 15

The cloudify.relationships.connected_to_shared_resource Relationship Type

As an extension of cloudify.relationships.connected_to relationship type, this can only target a node of type of SharedResource. This relationship will allow running any workflow (custom or not) ,which is defined in the target node’s deployment, as a part from establish and unlink relationship lifecycle. With support for scaling the relationship according to cloudify.relationships.connected_to features. Also if the SharedResource node has been created with different Cloudify client connection, those settings will be taken from the node properties if exists else it will use default Cloudify client.

Relationship settings:

Simple example

node_templates:
  shared_resource_node:
    type: cloudify.nodes.SharedResource
    properties:
      resource_config:
        deployment:
            id: shared_resource_deployment

  app:
    type: cloudify.nodes.WebServer
    relationships:
      - type: cloudify.relationships.connected_to_shared_resource:
        target: shared_resource_node
        target_interfaces:
          cloudify.interfaces.relationship_lifecycle:
            establish:
              inputs:
                workflow_id: custom_workflow
                parameters: {input: 'x'}
            unlink:
              inputs:
                workflow_id: un_custom_workflow
                timeout: 15

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 for which the value can be either all_to_all or all_to_one (The default value is all_to_all). The following diagrams make their semantics clearer.

all_to_all

Consider the following 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, there are two node instances of the application node and two node instances of the database node. All application node instances are connected to all database node instances. This would have relevance in the case of two Node.js application servers that must connect to two memcached nodes, for example.

all_to_all diagram

all_to_one

Consider the following 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, there are two node instances of the application node and two node instances of the database node. All application node instances are connected to one database node instance (selected at random). This would have relevance in the case of two Node.js application servers that must add themselves as users on a single cassandra node, for example.

all_to_one diagram

Relationship Instances

In the case in which you have a node with two instances and two relationships configured for them, when a deployment is created, the node instances are instantiated in the model. In the same way that 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 as follows:

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 dictionary of interfaces.
target_interfaces no dict A dictionary 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, a relationship type called app_connected_to_db is created that 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 specific node:

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, the postconfigure lifecycle operation in the source_connected_to_target relationship type is configured once in its source_interfaces section and in the target_interfaces section. This means that 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 assumes that 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 is executed after the entire set of lifecycle operations of the target node are executed and completed. When using the uninstall workflow, the opposite is true.

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

Relationships Extensions

For building your application’s blueprints in a layered architecture, building blocks approach, the ability to wire in different component’s relationships is very useful and allows good separation of your application to self dependent blocks. Which can allow creating a complex inter-service relationships and full application view.

Example:

imports:
  - http://www.getcloudify.org/spec/cloudify/5.0.0/types.yaml

inputs:
  server_ip:
    description: >
      The ip of the server the application will be deployed on.
  agent_user:
    description: >
      User name used when SSH-ing into the started machine.
  agent_private_key_path:
    description: >
      Path to a private key that resides on the management machine.
      SSH-ing into agent machines will be done with this key.

node_templates:
  vm:
    type: cloudify.nodes.Compute
    properties:
      ip: { get_input: server_ip }
      agent_config:
        user: { get_input: agent_user }
        key: { get_input: agent_private_key_path }
        
imports:
    - http://www.getcloudify.org/spec/cloudify/5.0.0/types.yaml

inputs:
  webserver_port:
    description: >
      The HTTP web server port.
    default: 8080

node_templates:
  http_web_server:
    type: cloudify.nodes.WebServer
    properties:
      port: { get_input: webserver_port }
    relationships:
      - type: cloudify.relationships.contained_in
        target: vm
    interfaces:
      cloudify.interfaces.lifecycle:
        configure: scripts/configure.sh
        start: scripts/start.sh
        stop: scripts/stop.sh
imports:
  - cloud_infrastructure--blueprint:vm
  - service--blueprint:http_service

node_templates:
  service--http_web_server:
    relationships:
      - type: cloudify.relationships.contained_in
        target: cloud_infrastructure--vm

For more information about service composition please check out in depth look.