1 # Component specification (Common elements)
3 This page describes component specification sections that are common (or nearly) to both Docker and CDAP.
6 Metadata refers to the properties found under the `self` JSON. This group of properties are used to uniquely identify this component specification and identify the component that this specification is used to capture. The metadata section, represented under `self`, is used to uniquely identify your component among all components in the catalog.
8 From the specification example above:
13 "name": "asimov.component.kpi_anomaly",
14 "description": "Classifies VNF KPI data as anomalous",
15 "component_type": "docker"
19 Here is a breakdown of the schema:
21 Property Name | Type | Description
22 ------------- | ---- | -----------
23 version | string | *Required*. Semantic version for this specification
24 name | string | *Required*. Full name of this component which is also used as this component's catalog id. The name includes a namespace that is dot-separated.
25 description | string | Human-readable text blurb describing the component and the components functional purpose.
26 component_type | string | *Required*. Identify what containerization technology this component uses: `docker` or `cdap`.
29 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](/components/data-formats.md).
32 * The `streams` JSON is for specifying that you produce data that can be consumed by other components, and the streams you expect to subscribe to 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.
33 * 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.
34 * Streams have anonymous publish/subscribe semantics, which decouples the production of information from its consumption.
35 * In general, components are not aware of who they are communicating with.
36 * Instead, components that are interested in data subscribe to the relevant stream; components that generate data publish to the relevant stream.
37 * There can be multiple publishers and subscribers to a stream. Streams are intended for unidirectional, streaming communication.
39 Streams interfaces that implement an HTTP endpoint must support POST.
41 Streams are split into:
43 Property Name | Type | Description
44 ------------- | ---- | -----------
45 subscribes | JSON list | *Required*. List of all available stream interfaces that this component has that can be used for subscribing
46 publishes | JSON list | *Required*. List of all stream interfaces that this component will publish onto
50 From the example specification:
55 "format": "dcae.vnf.kpi",
57 "route": "/data", // for CDAP this value is not used
64 This describes that `asimov.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`.
66 The JSON object schema used in `subscribes`:
68 Property Name | Type | Description
69 ------------- | ---- | -----------
70 format | string | *Required*. Data format id of the data format that is used by this interface
71 version | string | *Required*. Data format version of the data format that is used by this interface
72 route | string | *Required*. The HTTP route that this interface listens on
73 type | string | *Required*. Type of stream: `http`, `message_router`, `data_router`
77 Message router subscribers are http clients rather than http services and performs a http `GET` call. Thus, message router subscribers description is structured like message router publishers and requires `config_key`:
82 "format": "dcae.some-format",
84 "config_key": "some_format_handle",
85 "type": "message router"
93 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 your subscriber to the provisioned feed. Developers must also provide a `config_key` because there is dynamic configuration information associated with the feed that your application will need e.g. username and password. See the page on [DMaaP connection objects](../dcae-cli/dmaap-connection-objects) for more details on the configuration information.
95 Example (not tied to the larger example):
100 "config_key": "some-sub-dr",
101 "format": "sandbox.platform.any",
102 "route": "/identity",
103 "type": "data_router",
112 From the example specification:
118 "format": "asimov.format.integerClassification",
120 "config_key": "prediction",
127 This describes that `asimov.component.kpi_anomaly` publishes by making POST requests to streams that support the data format `asimov.format.integerClassification` version `1.0.0`.
129 The JSON object schema used in `publishes`:
131 Property Name | Type | Description
132 ------------- | ---- | -----------
133 format | string | *Required*. Data format id of the data format that is used by this interface
134 version | string | *Required*. Data format version of the data format that is used by this interface
135 config_key | string | *Required*. The JSON key in the generated application configuration that will be used to pass the downstream component connection information.
136 type | string | *Required*. Type of stream: `http`, `message router`
140 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 your application will need to receive e.g. publish url, username, password. See the page on [DMaaP connection objects](../dcae-cli/dmaap-connection-objects) for more details on the configuration information.
142 Example (not tied to the larger example):
148 "config_key": "some-pub-dr",
149 "format": "sandbox.platform.any",
150 "type": "data_router",
158 * The publish / subscribe model is a very flexible communication paradigm, but its many-to-many one-way transport is not appropriate for RPC
159 request / reply interactions, which are often required in a distributed system.
160 * Request / reply is done via a Service, which is defined by a pair of messages: one for the request and one for the reply.
162 Services are split into:
164 Property Name | Type | Description
165 ------------- | ---- | -----------
166 calls | JSON list | *Required*. List of all service interfaces that this component will call
167 provides | JSON list | *Required*. List of all service interfaces that this component exposes and provides
170 The JSON `services/calls` is for specifying that your component relies on an HTTP(S) service---your component sends that service an HTTP request, and that service responds with an HTTP reply.
171 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`.
173 From the example specification:
178 "config_key": "vnf-db",
180 "format": "dcae.vnf.meta",
184 "format": "dcae.vnf.kpi",
192 This describes that `asimov.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`.
194 The JSON object schema used in `calls`:
196 Property Name | Type | Description
197 ------------- | ---- | -----------
198 request | JSON object | *Required*. Description of the expected request for this downstream interface
199 response | JSON object | *Required*. Description of the expected response for this downstream interface
200 config_key | string | *Required*. The JSON key in the generated application configuration that will be used to pass the downstream component connection information.
202 The JSON object schema for both `request` and `response`:
204 Property Name | Type | Description
205 ------------- | ---- | -----------
206 format | string | *Required*. Data format id of the data format that is used by this interface
207 version | string | *Required*. Data format version of the data format that is used by this interface
211 From the example specification:
217 "route": "/score-vnf",
219 "format": "dcae.vnf.meta",
223 "format": "asimov.format.integerClassification",
230 This describes that `asimov.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 `asimov.format.integerClassification` version `1.0.0`.
232 The JSON object schema used in `provides`:
234 Property Name | Type | Description
235 ------------- | ---- | -----------
236 request | JSON object | *Required*. Description of the expected request for this interface
237 response | JSON object | *Required*. Description of the expected response for this interface
238 route | string | *Required*. The HTTP route that this interface listens on
240 The JSON object schema for both `request` and `response`:
242 Property Name | Type | Description
243 ------------- | ---- | -----------
244 format | string | *Required*. Data format id of the data format that is used by this interface
245 version | string | *Required*. Data format version of the data format that is used by this interface
247 Note, for CDAP, there is a slight variation due to the way CDAP exposes services:
249 "provides":[ // note this is a list of JSON
253 "service_name":"name CDAP service",
254 "service_endpoint":"greet", // E.g the URL is /services/service_name/methods/service_endpoint
255 "verb":"GET" // GET, PUT, or POST