What is Component Specification?

This page will discuss categories defined in component specification schema and their usage.

Meta Schema Definition

The “Meta Schema” implementation defines how component specification JSON schemas can be written to define user input. It is itself a JSON schema (thus it is a “meta schema”). It requires the name of the component entry, component type (either ‘cdap’ or ‘docker’) and a description under “self” object. The meta schema version must be specified as the value of the “version” key. Then the input schema itself is described.

There are four types of schema descriptions objects - jsonschema for inline standard JSON Schema definitions of JSON inputs, delimitedschema for delimited data input using a JSON description defined by AT&T, unstructured for unstructured text, and reference that allows a pointer to another artifact for a schema. The reference allows for XML and Protocol Buffer schema, but can be used as a pointer to JSON, Delimited Format, and Unstructured schemas as well.

Component Metadata

Metadata refers to the properties found under the self JSON. This group of properties is used to uniquely identify this component specification and identify the component that this specification is used to capture.

Example:

"self": {
    "version": "1.0.0",
    "name": "yourapp.component.kpi_anomaly",
    "description": "Classifies VNF KPI data as anomalous",
    "component_type": "docker"
},

self Schema:

Property Name	Type	Description
version	string	Required. Semantic version for this specification
name	string	Required. Full name of this component which is also used as this component’s catalog id.
description	string	Required Human-readable text describing the component and the components functional purpose.
component_type	string	Required Identify what containerization technology this component uses: docker or cdap.

Interfaces

Interfaces are the JSON objects found under the streams key and the services key. These are used to describe the interfaces that the component uses and the interfaces that the component provides. The description of each interface includes the associated data format.

Streams

The streams JSON is for specifying data produced for consumption by other components, and the streams expected to subscribe to that is produced by other components. These are “fire and forget” type interfaces where the publisher of a stream does not expect or parse a response from the subscriber.
The term stream here is abstract and neither refers to “CDAP streams” or “DMaaP feeds”. While a stream is very likely a DMaaP feed, it could be a direct stream of data being routed via HTTP too. It abstractly refers to a sequence of data leaving a publisher.
Streams have anonymous publish/subscribe semantics, which decouples the production of information from its consumption. Like the component specification, the data format specification is represented/validated against this Data Format json schema
In general, components are not aware of who they are communicating with.
Instead, components that are interested in data, subscribe to the relevant stream; components that generate data publish to the relevant stream.
There can be multiple publishers and subscribers to a stream. Streams are intended for unidirectional, streaming communication.

Streams interfaces that implement an HTTP endpoint must support POST.

Streams are split into:

Property Name	Type	Description
subscribes	JSON list	Required. List of all available stream interfaces that this component has that can be used for subscribing
publishes	JSON list	Required. List of all stream interfaces that this component will publish onto

Subscribes

Example:

"streams": {
    "subscribes": [{
        "format": "dcae.vnf.kpi",
        "version": "1.0.0",
        "route": "/data",        // for CDAP this value is not used
        "type": "http"
    }],
...
}

This describes that yourapp.component.kpi_anomaly exposes an HTTP endpoint called /data which accepts requests that have the data format of dcae.vnf.kpi version 1.0.0.

subscribes Schema:

Property Name	Type	Description
format	string	Required. Data format id of the data format that is used by this interface
version	string	Required. Data format version of the data format that is used by this interface
route	string	Required for HTTP and data router. The HTTP route that this interface listens on
config_key	string	Required for message_routerand data router. The HTTP route that this interface listens on
type	string	Required. Type of stream: `http` , `message_router` , `data_router` , `kafka`

Message router

Message router subscribers are http clients rather than http services and performs a http a GET call. Thus, message router subscribers description is structured like message router publishers and requires config_key:

"streams": {
    "subscribes": [{
        "format": "dcae.some-format",
        "version": "1.0.0",
        "config_key": "some_format_handle",
        "type": "message router"
    }],
...
}

Data router

Data router subscribers are http or https services that handle PUT requests from data router. Developers must provide the route or url path/endpoint that is expected to handle data router requests. This will be used to construct the delivery url needed to register the subscriber to the provisioned feed. Developers must also provide a config_key because there is dynamic configuration information associated with the feed that the application will need e.g. username and password. See the page on DMaaP connection objects for more details on the configuration information.

Example (not tied to the larger example):

"streams": {
    "subscribes": [{
        "config_key": "some-sub-dr",
        "format": "sandbox.platform.any",
        "route": "/identity",
        "type": "data_router",
        "version": "0.1.0"
    }],
...
}

Kafka

Kafka subscribers are clients fetching data directly from kafka.

config_key:

"streams": {
    "subscribes": [{
        "format": "dcae.some-format",
        "version": "1.0.0",
        "config_key": "some_format_handle",
        "type": "kafka"
    }],
...
}

Publishes

Example:

"streams": {
...
    "publishes": [{
        "format": "yourapp.format.integerClassification",
        "version": "1.0.0",
        "config_key": "prediction",
        "type": "http"
    }]
},

This describes that yourapp.component.kpi_anomaly publishes by making POST requests to streams that support the data format yourapp.format.integerClassification version 1.0.0.

publishes Schema:

Property Name	Type	Description
format	string	Required. Data format id of the data format that is used by this interface
version	string	Required. Data format version of the data format that is used by this interface
config_key	string	Required. The JSON key in the generated applicat ion configuration that will be used to pass the downstream component’s (the subscriber’s) connection information.
type	string	Required. Type of stream: `http` , `message_router` , `data_router` , `kafka`

Message router

Message router publishers are http clients of DMaap message_router. Developers must provide a config_key because there is dynamic configuration information associated with the feed that the application needs to receive e.g. topic url, username, password. See the page on DMaaP connection objects for more details on the configuration information.

Example (not tied to the larger example):

"streams": {
...
    "publishes": [{
        "config_key": "some-pub-mr",
        "format": "sandbox.platform.any",
        "type": "message_router",
        "version": "0.1.0"
    }]
}

Data router

Data router publishers are http clients that make PUT requests to data router. Developers must also provide a config_key because there is dynamic configuration information associated with the feed that the application will need to receive e.g. publish url, username, password. See the page on DMaaP connection objects for more details on the configuration information.

Example (not tied to the larger example):

"streams": {
...
    "publishes": [{
        "config_key": "some-pub-dr",
        "format": "sandbox.platform.any",
        "type": "data_router",
        "version": "0.1.0"
    }]
}

Kafka

Kafka publishers are clients publishing data directly to kafka.

config_key:

"streams": {
    "publishes": [{
        "format": "dcae.some-format",
        "version": "1.0.0",
        "config_key": "some_format_handle",
        "type": "kafka"
    }],
...
}

Quick Reference

Refer to this Quick Reference for a comparison of the Streams ‘Publishes’ and ‘Subscribes’ sections.

Services

The publish / subscribe model is a very flexible communication paradigm, but its many-to-many one-way transport is not appropriate for RPC request / reply interactions, which are often required in a distributed system.
Request / reply is done via a Service, which is defined by a pair of messages: one for the request and one for the reply.

Services are split into:

Property Name	Type	Description
calls	JSON list	Required. List of all service interfaces that this component will call
provides	JSON list	Required. List of all service interfaces that this component exposes and provides

Calls

The JSON services/calls is for specifying that the component relies on an HTTP(S) service—the component sends that service an HTTP request, and that service responds with an HTTP reply. An example of this is how string matching (SM) depends on the AAI Broker. SM performs a synchronous REST call to the AAI broker, providing it the VMNAME of the VNF, and the AAI Broker responds with additional details about the VNF. This dependency is expressed via services/calls. In contrast, the output of string matching (the alerts it computes) is sent directly to policy as a fire-and-forget interface, so that is an example of a stream.

Example:

"services": {
    "calls": [{
        "config_key": "vnf-db",
        "request": {
            "format": "dcae.vnf.meta",
            "version": "1.0.0"
            },
        "response": {
            "format": "dcae.vnf.kpi",
            "version": "1.0.0"
            }
    }],
...
}

This describes that yourapp.component.kpi_anomaly will make HTTP calls to a downstream component that accepts requests of data format dcae.vnf.meta version 1.0.0 and is expecting the response to be dcae.vnf.kpi version 1.0.0.

calls Schema:

Property Name	Type	Description
request	JSON object	Required. Description of the expected request for this downstream interface
response	JSON object	Required. Description of the expected response for this downstream interface
config_key	string	Required. The JSON key in the generated applicat ion configuration that will be used to pass the downstream componen t connection information.

The JSON object schema for both request and response:

Property Name	Type	Description
format	string	Required. Data format id of the data format that is used by this interface
version	string	Required. Data format version of the data format that is used by this interface

Provides

Example:

"services": {
...
    "provides": [{
        "route": "/score-vnf",
        "request": {
            "format": "dcae.vnf.meta",
            "version": "1.0.0"
            },
        "response": {
            "format": "yourapp.format.integerClassification",
            "version": "1.0.0"
            }
    }]
},

This describes that yourapp.component.kpi_anomaly provides a service interface and it is exposed on the /score-vnf HTTP endpoint. The endpoint accepts requests that have the data format dcae.vnf.meta version 1.0.0 and gives back a response of yourapp.format.integerClassification version 1.0.0.

provides Schema for a Docker component:

Property Name	Type	Description
request	JSON object	Required. Description of the expected request for this interface
response	JSON object	Required. Description of the expected response for this interface
route	string	Required. The HTTP route that this interface listens on

The JSON object schema for both request and response:

Property Name	Type	Description
format	string	Required. Data format id of the data format that is used by this interface
version	string	Required. Data format version of the data format that is used by this interface

Note, for CDAP, there is a slight variation due to the way CDAP exposes services:

"provides":[                             // note this is a list of JSON
   {
      "request":{  ...},
      "response":{  ...},
      "service_name":"name CDAP service",
      "service_endpoint":"greet",         // E.g the URL is /services/service_name/methods/service_endpoint
      "verb":"GET"                        // GET, PUT, or POST
   }
]

provides Schema for a CDAP component:

Property Name	Type	Description
request	JSON object	Required. Description of the expected request data format for this interface
response	JSON object	Required. Description of the expected response for this interface
service_name	string	Required. The CDAP service name (eg “Greeting”)
service_end point	string	Required. The CDAP service endpoint for this service_name (eg “/greet” )
verb	string	Required. ‘GET’, ‘PUT’ or ‘POST’

Parameters

parameters is where to specify the component’s application configuration parameters that are not connection information.

Property Name	Type	Description
parameters	JSON array	Each entry is a parameter object

Parameter object has the following available properties:

Property Name	Type	Description	Default
name	string	Required. The property name that will be used as the key in the generated config
value	any	Required. The default value for the given parameter
description	string	Required. Human-readable text describing the parameter like what its for
type	string	The required data type for the parameter
required	boolean	An optional key that declares a parameter as required (true) or not (false)	true
constraints	array	The optional list of sequence d constraint clauses for the parameter. See below
entry_schema	string	The optional key that is used to declare the name of the Datatype definition for entries of set types such as the TOSCA ‘list’ or ‘map’. Only 1 level is supported at this time
designer_editable	boolean	An optional key that declares a parameter to be editable by designer (true) or not (false)
sourced_at_deployment	boolean	An optional key that declares a parameter’s value to be assigned at deployment time (true)
policy_editable	boolean	An optional key that declares a parameter to be editable by policy (true) or not (false)
policy_schema	array	The optional list of schema definitions used for policy. See below

Example:

"parameters": [
    {
        "name": "threshold",
        "value": 0.75,
        "description": "Probability threshold to exceed to be anomalous"
    }
]

Many of the parameter properties have been copied from TOSCA model property definitions and are to be used for service design composition and policy creation. See section 3.5.8 *Property definition*.

The property constraints is a list of objects where each constraint object:

Property Name	Type	Description
equal		Constrains a property or parameter to a value equal to (‘=’) the value declared
greater_than	number	Constrains a property or paramete r to a value greater than (‘>’) the value declared
greater_or_equal	number	Constrains a property or parameter to a value greater than or equal to (‘>=’) the value declared
less_than	number	Constrains a property or parameter to a value less than (‘<’) the value declared
less_or_equal	number	Constrains a property or parameter to a value less than or equal to (‘<=’) the value declared
valid_values	array	Constrains a property or parameter to a value that is in the list of declared values
length	number	Constrains the property or parameter to a value of a given length
min_length	number	Constrains the property or parameter to a value to a minimum length
max_length	number	Constrains the property or parameter to a value to a maximum length

threshold is the configuration parameter and will get set to 0.75 when the configuration gets generated.

The property policy_schema is a list of objects where each policy_schema object:

Property Name	Type	Description	Default
name	string	Required. parameter name
value	string	default value for the parameter
description	string	parameter description
type	enum	Required. data type of the parameter, ‘string’ , ‘number’ , ‘boolean ’, ‘datetime’, ‘list’, or ‘map’
required	boolean	is parameter required or not?	true
constraints	array	The optional list of sequenced constraint clauses for the parameter. See above
entry_schema	string	The optional key that is used to declare the name of the Datatype definition for certain types. entry_schema must be defined when the type is either list or map. If the type is list and the entry type is a simple type (string, number, bookean, datetime ), follow with an string to describe the entry
	If the type is list and the entry type is a map, follow with an array to describe the keys for the entry map
	If the type is list and the entry type is a list , that is not currently supported
	If the type is map, follow with an aray to describe the keys for the map

Artifacts

artifacts contains a list of artifacts associated with this component. For Docker, this is the full path (including the registry) to the Docker image. For CDAP, this is the full path to the CDAP jar.

Property Name	Type	Description
artifacts	JSON array	Each entry is a artifact object

artifact Schema:

Property Name	Type	Description
uri	string	Required. Uri to the artifact, full path
type	string	Required. `docker image` or `jar`

Auxilary

New V3 version of component spec schema introduced - https://github.com/onap/dcaegen2-platform/blob/master/mod/component-json-schemas/component-specification/dcae-cli-v3/component-spec-schema.json

Added new “helm” object under “auxilary_docker” properties
- Includes “applicationEnv”
- Includes “service” definition
Readiness Configuration support
- docker_healthcheck_http
  - Added HTTP/HTTPS for supported protocol enum list
  - Added “port”
  - Added “initialDelaySeconds”
- docker_healthcheck_script
  - Added “initialDelaySeconds”

Health check

Component developers are required to provide a way for the platform to periodically check the health of their running components. The details of the definition used by your component is to be provided through the Docker auxiliary specification.

The information contained in the auxilary_docker field is the Docker component specification schema. Some properties of the docker component specification include -

healthcheck : Defines the health check that Consul should perform for this component

log_info : Component specific details for logging, includes the path in the container where logs are written that can also be used for logstash/kibana style reporting.

ports : Port mapping to be used for Docker containers. Each entry is of the format <container port>:<host port>.

tls_info : Component information for use of tls certificates, where they will be available, whether or not to use them

policy : Information for Policy configuration and reconfiguration

databases: Information about databases the application should connect to

volumes: Contains information on volume mapping for the docker containers

Schema portion:

"auxilary_docker": {
  "title": "Docker component specification schema",
  "type": "object",
  "properties": {
    "healthcheck": {
      "description": "Define the health check that Consul should perfom for this component",
      "type": "object",
      "oneOf": [
        { "$ref": "#/definitions/docker_healthcheck_http" },
        { "$ref": "#/definitions/docker_healthcheck_script" }
      ]
    },
    "ports": {
      "description": "Port mapping to be used for Docker containers. Each entry is of the format <container port>:<host port>.",
      "type": "array",
      "items": {
        "type": "string"
      }
    },
    "log_info": {
      "description": "Component specific details for logging",
      "type": "object",
      "properties": {
        "log_directory": {
          "description": "The path in the container where the component writes its logs. If the component is following the EELF requirements, this would be the directory where the four EELF files are being written. (Other logs can be placed in the directory--if their names in '.log', they'll also be sent into ELK.)",
          "type": "string"
        },
        "alternate_fb_path": {
          "description": "By default, the log volume is mounted at /var/log/onap/<component_type> in the sidecar container's file system. 'alternate_fb_path' allows overriding the default.  Will affect how the log data can be found in the ELK system.",
          "type": "string"
        }
      },
      "additionalProperties": false
    },
    "tls_info": {
      "description": "Component information to use tls certificates",
      "type": "object",
      "properties": {
        "cert_directory": {
          "description": "The path in the container where the component certificates will be placed by the init container",
          "type": "string"
        },
        "use_tls": {
          "description": "Boolean flag to determine if the application is using tls certificates",
          "type": "boolean"
        },
        "use_external_tls": {
          "description": "Boolean flag to determine if the application is using tls certificates for external communication",
          "type": "boolean"
        }
      },
      "required": [
        "cert_directory","use_tls"
      ],
      "additionalProperties": false
    },
    "databases": {
      "description": "The databases the application is connecting to using the pgaas",
      "type": "object",
      "additionalProperties": {
        "type": "string",
        "enum": [
          "postgres"
        ]
      }
    },
    "policy": {
      "properties": {
        "trigger_type": {
          "description": "Only value of docker is supported at this time.",
          "type": "string",
          "enum": ["docker"]
        },
        "script_path": {
          "description": "Script command that will be executed for policy reconfiguration",
          "type": "string"
        }
      },
      "required": [
        "trigger_type","script_path"
      ],
      "additionalProperties": false
    },
    "volumes": {
      "description": "Volume mapping to be used for Docker containers. Each entry is of the format below",
      "type": "array",
      "items": {
        "type": "object",
        "oneOf": [
          { "$ref": "#/definitions/host_path_volume" },
          { "$ref": "#/definitions/config_map_volume" }
        ]
      }
    }
  },
  "required": [
    "healthcheck"
  ],
  "additionalProperties": false
}