Microservice Simulator

The Microservice Simulator lets you simulate a distributed Node.js microservice architecture by running multiple service instances and orchestrating complex workflows between them. You define and execute workflows involving HTTP requests, delays, logging, and code execution using a developer-friendly JavaScript API, making it a powerful tool for testing and prototyping microservice interactions.

Key Features

• Multi-Instance Simulation: Easily spin up multiple simulated microservices, each with its own configuration.
• Flexible Workflow Builder: Compose workflows using a modern JavaScript API.
• Chained and Asynchronous Actions: Workflows can trigger nested requests, custom code, and more.
• Code-First Configuration: Define all workflows and microservice setups programmatically.

How It Works

You define workflows as arrays of actions (steps), which can include:

• Sending HTTP requests to other simulated microservices.
• Executing custom JavaScript code (with access to a shared context and logger).
• Introducing delays to simulate real-world timing.
• Logging messages for debugging or monitoring.
• Returning custom data for further processing.

Each microservice instance runs as a separate Node.js process, and workflows can trigger requests between them.

Getting Started

Prerequisites

• Node.js (v18 or higher)
• npm

Installation

1. Clone the repository:

   git clone https://github.com/motero2k/microservice-simulator.git
   cd microservice-simulator

2. Install dependencies:

   npm install

Running the Simulator

You can run the demo scenario (see examples/request-builder-demo.js):

node examples/request-builder-demo.js

Or, to start a microservice instance directly:

npm start

Or, for development with auto-reload:

npm run dev

Project Structure

• src/ - Main simulator server code.
• lib/request-builder.js - Functional API for building workflows.
• lib/simulator.js - Orchestrates running workflows and microservices.
• examples/request-builder-demo.js - Example workflow using the builder API.

Defining Workflows

You define workflows using the JavaScript builder API:

import {
  httpRequest, Microservice, log, wait, code, returnData, setContext, multi
} from "./lib/request-builder.js";

const myService = Microservice({ SERVICE_NAME: "MyService", PORT: 3000 });

const workflow = httpRequest({ //first action should be httpRequest to one of the microservices
  microservice: myService,
  path: "/api/do-something",
  actions: [
    log({ message: "Starting workflow" }),
    wait({ duration: 500 }),
    code(() => { /* custom JS code */ }),
    returnData({ status: "done" })
  ]
});

runSimulation(workflow).then(result => {
  console.log("Workflow completed with result:", result);
}).catch(err => {
  console.error("Workflow failed:", err);
});

Key Actions

• log: Logs a message.
• wait: Introduces a delay (in milliseconds).
• http: Sends an HTTP request to a specified microservice or origin. Nested actions can be defined.
• code: Executes custom JavaScript code (with access to logger and context).
• return: Returns custom data for further processing.
• set: Sets a value in the shared context.
• multi: Runs multiple actions, optionally with repeat/wait.

Example

See examples/request-builder-demo.js for a full workflow example using the builder API.

Scripts

• npm start - Start a microservice instance (src/index.js).
• npm run dev - Start with auto-reload (development).
• npm run demo - Run the example workflow.

Configuration

Microservice Instances

Define microservice instances in code using the Microservice helper:

const myService = Microservice({ SERVICE_NAME: "MyService", PORT: 3000 });

Workflows

Workflows are defined in code using the builder API (see above).
JSON configuration is no longer supported or recommended.

Contributing

Contributions are welcome! Feel free to open issues or submit pull requests.

License

This project is licensed under the ISC License.