14. Context Broker Federation

A “Federation Broker” is a Broker in a distributed setup with an associated Context Registry (e.g. - entity is created in one Scorpio instance and processed by other Scorpio instance without storing the data locally). This Context Providers and request forwarding functionality is a kind of “pull” federation (in which one Scorpio instance forwards a query/update to another Scorpio instance).

Let’s illustrate with an example

Consider the following setup: two context broker instances running in the same machine (of course, this is not a requirement but makes things simpler to test this feature), on ports 9090 and 9091 respectively and using different databases (named A and B to be brief).

Let’s start each instance and consider current setup is as follows:

Federator CB is deployed on http://federator_ip:9090 Instance1 CB is deployed on http://instance1_ip:9091

Step 1. Create a simple entity in instance1

POST http://instance1_ip:9091/ngsi-ld/v1/entities
Content-Type: application/ld+json
Body:
{
    "id": "urn:ngsi-ld:AirQuality:test1",
    "type": "AirQuality",
    "co": {
        "type": "Property",
        "value": 0.2,
        "observedAt": "2023-10-17T04:25:00Z",
        "unitCode": "GP"
    },
    "@context": [
        "https://uri.etsi.org/ngsi-ld/v1/ngsi-ld-core-context-v1.7.jsonld"
    ]
}

Step 2. Register the instance1 into the federator broker.

POST http://federator_ip:9090/ngsi-ld/v1/csourceRegistrations
Content-Type: application/ld+json
Body:
{
    "id": "urn:ngsi-ld:ContextSourceRegistration:test001",
    "type": "ContextSourceRegistration",
    "information": [
        {
            "entities": [
                {
                    "type": "AirQuality"
                }
            ]
        }
    ],
    "endpoint": "http://instance1_ip:9091",
    "@context": [
        "https://uri.etsi.org/ngsi-ld/v1/ngsi-ld-core-context-v1.7.jsonld"
    ]
}

Step 3. Query the AirQuality entities in both Context Brokers.

• Instance1 Request:

GET http://instance1_ip:9091/ngsi-ld/v1/entities/?type=AirQuality
Accept: application/ld+json

Response:

[
    {
        "id": "urn:ngsi-ld:AirQuality:test1",
        "type": "AirQuality",
        "co": {
            "type": "Property",
            "value": 0.2,
            "observedAt": "2023-10-17T04:25:00Z",
            "unitCode": "GP"
        },
        "@context": [
            "https://uri.etsi.org/ngsi-ld/v1/ngsi-ld-core-context-v1.7.jsonld"
        ]
    }
]

• Federator Request:

GET http://federator_ip:9090/ngsi-ld/v1/entities/?type=AirQuality
Accept: application/ld+json

Response:

[
    {
        "id": "urn:ngsi-ld:AirQuality:test1",
        "type": "AirQuality",
        "co": {
            "type": "Property",
            "value": 0.2,
            "observedAt": "2023-10-17T04:25:00Z",
            "unitCode": "GP"
        },
        "@context": [
            "https://uri.etsi.org/ngsi-ld/v1/ngsi-ld-core-context-v1.7.jsonld"
        ]
    }
]

Here, we can see a simple use case of federation setup in which entity is located in Instance1 Scorpio broker and forwarded to the Federator Scorpio Broker.