connecting_orion.md

Connecting Orion Context Broker and Cygnus

Cygnus takes advantage of the subscription-notification mechanism of Orion Context Broker. Specifically, Cygnus needs to be notified each time certain entity's attributes change, and in order to do that, Cygnus must subscribe to those entity's attribute changes.

You can make a subscription to Orion on behalf of Cygnus by using a curl command or any other REST client. In the following example, we assume both Orion and Cygnus run in localhost, and Cygnus is listening in the TCP/5050 port:

(curl localhost:1026/v1/subscribeContext -s -S --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'Fiware-Service: vehicles' --header 'Fiware-ServicePath: /4wheels' -d @- | python -mjson.tool) <<EOF
{
    "entities": [
        {
            "type": "car",
            "isPattern": "false",
            "id": "car1"
        }
    ],
    "attributes": [
        "speed",
        "oil_level"
    ],
    "reference": "http://localhost:5050/notify",
    "duration": "P1M",
    "notifyConditions": [
        {
            "type": "ONCHANGE",
            "condValues": [
                "speed"
            ]
        }
    ],
    "throttling": "PT1S"
}
EOF

Which means: Each time the the 'car1' entity, of type 'car', which is registered under the service/tenant 'vehicles', subservice '/4wheels', changes its value of 'speed' then send a notification to http://localhost:5050/notify (where Cygnus will be listening) with the 'speed' and 'oil_level' values. This subscription will have a duration of one month, and please, do not send me notifications more than once per second.