moleculer

来源：go-interview / Source

Components in Moleculer

1. Services: Core units of functionality, containing actions and event handlers.
2. Actions: Methods exposed by services for direct invocation.
3. Events: Mechanism for decoupled communication between services.
4. Event Bus: Centralized system for managing events.
5. API Gateway: Entry point for external clients, exposing REST/GraphQL endpoints.
6. Transporter: Handles communication between nodes in a distributed setup.
7. Middleware: Custom logic that can be applied to actions or events.
8. Broker: The core of Moleculer, managing services, events, and communication.

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Example Flow Diagram

Below is an example flow of a Moleculer-based application:

sequenceDiagram
    participant Client
    participant Gateway as API Gateway
    participant ServiceA as Service A
    participant ServiceB as Service B
    participant EventBus as Event Bus

    Client->>Gateway: HTTP Request (REST/GraphQL)
    Gateway->>ServiceA: Call Action (e.g., `getUser`)
    ServiceA->>ServiceB: Call Action (e.g., `getUserDetails`)
    ServiceB-->>ServiceA: Response (User Details)
    ServiceA-->>Gateway: Response (User Data)
    Gateway-->>Client: HTTP Response

    ServiceA->>EventBus: Emit Event (e.g., `user.updated`)
    EventBus->>ServiceB: Broadcast Event (e.g., `user.updated`)
    EventBus->>ServiceC: Broadcast Event (e.g., `user.updated`)

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Explanation of the Flow

1. Client Interaction:

   • The client sends an HTTP request to the API Gateway.
   • The Gateway forwards the request to the appropriate service (Service A).

2. Service Communication:

   • Service A calls an action in Service B to fetch additional data.
   • Service B processes the request and returns the response to Service A.

3. Event Emission:

   • After processing, Service A emits an event (user.updated) to the Event Bus.
   • The Event Bus broadcasts the event to all subscribed services (Service B, Service C).

4. Response to Client:

   • The final response is sent back to the client via the API Gateway.