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Astarte Message Hub

A central service that runs on (Linux) devices for collecting and delivering messages from N apps using 1 MQTT connection to Astarte.

Architecture

The Astarte Message Hub is the main component that shares the Astarte connection to the nodes attached to it. The communication between the Hub and nodes is based on gRPC which is great for scenarios like real-time communication, low-power, low-bandwidth systems, and multi-language environments. gRPC makes the most out of HTTP/2, with multiplexed streaming and binary protocol framing. In addition, it offers performance advantages through the Protobuf message structure and features built-in code generation capability, which enables a multi-language environment.

flowchart LR
  subgraph arch[  ]
    direction TB
    subgraph cloud[ ]
        style cloud fill:#00b0f1,stroke:#ffffff
        direction LR
        subgraph astarte[Astarte]
        style astarte fill:#127ab2,stroke:#ffffff,color:#fff
        end
    end
    subgraph device[   ]
    style device fill:#00b0f1, stroke:#ffffff
    direction TB
        astarte-mh[Astarte Message Hub]
            style astarte-mh fill:#127ab2,stroke:#ffffff,color:#fff
        astarte-mh <--> node1[Node 1]
        astarte-mh <--> node2[Node 2]
        astarte-mh <--> noden[Node...N]
        style node1 stroke:#ffffff
        style node2 stroke:#ffffff
        style noden stroke:#ffffff
    end
  end
  astarte <==> astarte-mh
  style arch fill:#25516e,stroke:#c4c4c4,stroke-width:1 px,color:#fff,stroke-dasharray: 2 1

GRPC MessageHub Service

Node

A node is an entity connected to Astarte Message Hub, it can receive/send messages from/to Astarte via the Message Hub. A node is uniquely identified by its Node UUID and has an Introspection that is a list of Interfaces used by it for exchanging data with Astarte.

message Node {
  string uuid = 1;
  repeated Interface introspection = 2;
}

Interface

Interfaces are a core concept of Astarte which defines how data is exchanged between Astarte and its peers.

message Interface {
  string name = 1;
  int32 major = 2;
  int32 minor = 3;
}

Attach Method

When a new node is connected to Message Hub, it will have to call Attach method to exchange data with Astarte. If the node was successfully attached, the method returns a gRPC stream into which the events received from Astarte(based on the declared Introspection) will be redirected.

service MessageHub {
  rpc Attach(Node) returns (stream NodeMessage) {}
  ....
}
sequenceDiagram
    participant Node1
    participant AstarteMessageHub
    participant Astarte
    Node1->>AstarteMessageHub: attach(node)
    AstarteMessageHub->>Astarte: sendIntrospection()
    
    alt when the introspection process fails
         AstarteMessageHub->>Node1: Unable to attach the node
    end
    
    Astarte->>AstarteMessageHub: Event data for node1
    AstarteMessageHub->>Node1: Event data
    Astarte->AstarteMessageHub: Event data for node1
    AstarteMessageHub->>Node1: Event data