Restarting Express & GRPC Servers In One Process

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Hey guys! Ever found yourself needing to run both an Express server and a gRPC server in a single process? It can be a pretty efficient way to manage resources, but what happens when one of those servers decides to take a nosedive? We need to ensure that if either server crashes, it can restart gracefully without bringing the whole ship down. Let's dive into how we can achieve this using TypeScript, Express, gRPC, and some clever microservices principles.

Understanding the Challenge

First off, let's break down the challenge. Running multiple servers within the same process can seem like a neat optimization. Think about it: shared memory space, potentially faster inter-service communication, and a single deployment unit. However, this also means that a single unhandled exception or fatal error in one server can bring down the entire process, taking both servers offline. Not ideal, right?

Graceful restarts are the key here. We want our system to be resilient. If something goes wrong, we want the affected server to restart automatically, minimizing downtime and ensuring our application stays responsive. We also want to make sure that the restart process itself doesn't cause any further disruption. This means handling existing connections, finishing ongoing tasks, and then shutting down cleanly before starting up again. Think of it like a well-choreographed dance, not a chaotic scramble.

To make this happen, we'll need to employ a few strategies:

  • Process Management: We need a way to monitor our servers and automatically restart them if they crash. Tools like pm2, nodemon, or even Docker's restart policies can come in handy here.
  • Error Handling: Robust error handling is crucial. We need to catch unhandled exceptions and ensure they don't propagate and crash the entire process. Logging these errors is also vital for debugging and preventing future issues.
  • Graceful Shutdown: Before restarting a server, we need to give it a chance to finish what it's doing. This means closing active connections, completing ongoing requests, and cleaning up resources.
  • Health Checks: Implementing health checks allows us to monitor the status of our servers and ensure they are ready to handle traffic after a restart.

In the following sections, we'll explore how to implement these strategies using TypeScript, Express, and gRPC. We'll also touch on how microservices principles can guide our approach to building a resilient and scalable system.

Setting Up the Project

Alright, let's get our hands dirty and start building! First things first, we need to set up our project. We'll be using TypeScript, so make sure you have Node.js and npm (or yarn) installed. Let's create a new project directory and initialize a TypeScript project:

mkdir multi-server-app
cd multi-server-app
npm init -y
tsc --init

This will create a package.json file and a tsconfig.json file, which are essential for managing our project dependencies and TypeScript compilation. Next, we need to install the necessary packages:

npm install express @grpc/grpc-js @grpc/proto-loader typescript ts-node nodemon --save
npm install @types/express --save-dev

Here's a breakdown of what we're installing:

  • express: The classic Node.js web framework.
  • @grpc/grpc-js: The gRPC library for Node.js.
  • @grpc/proto-loader: A utility for loading Protocol Buffer definitions.
  • typescript: The TypeScript compiler.
  • ts-node: Allows us to run TypeScript files directly.
  • nodemon: Automatically restarts the server when file changes are detected (great for development).
  • @types/express: TypeScript definitions for Express.

Now, let's configure our tsconfig.json file. Open it up and make sure it includes the following settings (or similar):

{
  "compilerOptions": {
    "target": "es2016",
    "module": "commonjs",
    "outDir": "./dist",
    "esModuleInterop": true,
    "forceConsistentCasingInFileNames": true,
    "strict": true,
    "skipLibCheck": true
  }
}

These settings ensure that our TypeScript code is compiled correctly and that we have strict type checking enabled, which is always a good idea for catching errors early.

Finally, let's set up our package.json to include some convenient scripts for running our application:

{
  "name": "multi-server-app",
  "version": "1.0.0",
  "description": "",
  "main": "index.js",
  "scripts": {
    "build": "tsc",
    "start": "node dist/index.js",
    "dev": "nodemon src/index.ts"
  },
  "keywords": [],
  "author": "",
  "license": "ISC",
  "dependencies": {
    "@grpc/grpc-js": "^1.10.4",
    "@grpc/proto-loader": "^0.7.10",
    "express": "^4.19.2"
  },
  "devDependencies": {
    "@types/express": "^4.17.21",
    "nodemon": "^3.1.0",
    "ts-node": "^10.9.2",
    "typescript": "^5.4.2"
  }
}

With these scripts in place, we can use npm run build to compile our TypeScript code, npm start to run the compiled code, and npm run dev to start the server in development mode with automatic restarts.

Now that we have our project set up, we can start building our Express and gRPC servers. Let's move on to creating the Express server first.

Building the Express Server

The first server we'll tackle is the Express server. Express is a flexible and minimalist web application framework for Node.js, perfect for building RESTful APIs and handling HTTP requests. Let's create a simple Express server that we can use as a foundation.

Create a new file named src/express-server.ts. This is where we'll define our Express server. Here's a basic example:

import express, { Request, Response } from 'express';

const app = express();
const port = 3000;

app.get('/', (req: Request, res: Response) => {
  res.send('Hello from Express!');
});

const startExpressServer = () => {
  return new Promise<void>((resolve, reject) => {
    const server = app.listen(port, () => {
      console.log(`Express server listening at http://localhost:${port}`);
      resolve();
    }).on('error', (err) => {
      console.error('Express server error:', err);
      reject(err);
    });
  });
};

export { startExpressServer };

In this code, we're doing the following:

  1. Importing the express module and the Request and Response types.
  2. Creating an Express application instance.
  3. Defining a simple route that responds with "Hello from Express!" when accessed.
  4. Creating a function startExpressServer that starts the Express server and returns a Promise. This allows us to handle the server startup asynchronously and catch any errors that might occur.
  5. Adding an error listener to the server to log any errors that occur during server operation.

This is a basic Express server, but it gives us a solid foundation to build upon. Now, let's move on to creating our gRPC server.

Setting Up the gRPC Server

Next up, we'll set up our gRPC server. gRPC is a high-performance, open-source universal RPC framework that uses Protocol Buffers as its Interface Definition Language (IDL). It's great for building efficient and scalable microservices.

First, we need to define our service using Protocol Buffers. Create a new directory named proto and a file inside it called greeter.proto. This file will define our gRPC service.

syntax = "proto3";

package greeter;

service Greeter {
  rpc SayHello (HelloRequest) returns (HelloReply) {}
}

message HelloRequest {
  string name = 1;
}

message HelloReply {
  string message = 1;
}

This .proto file defines a simple Greeter service with a single method, SayHello, which takes a HelloRequest and returns a HelloReply. Now, we need to generate the gRPC code from this definition. We'll use the @grpc/proto-loader and @grpc/grpc-js libraries for this.

Create a new file named src/grpc-server.ts. This file will contain the logic for our gRPC server. Here’s how we can set it up:

import * as grpc from '@grpc/grpc-js';
import * as protoLoader from '@grpc/proto-loader';
import path from 'path';

const PROTO_PATH = path.resolve(__dirname, '../proto/greeter.proto');

const packageDefinition = protoLoader.loadSync(
    PROTO_PATH,
    {
        keepCase: true,
        longs: String,
        enums: String,
        defaults: true,
        oneofs: true
    });

const greeterProto: any = grpc.loadPackageDefinition(packageDefinition).greeter;

function sayHello(call: any, callback: any) {
    const name = call.request.name || 'World';
    callback(null, { message: 'Hello ' + name });
}

const startGrpcServer = () => {
    return new Promise<void>((resolve, reject) => {
        const server = new grpc.Server();
        server.addService(greeterProto.Greeter.service, { sayHello: sayHello });
        server.bindAsync('0.0.0.0:50051', grpc.ServerCredentials.createInsecure(), (err, port) => {
            if (err) {
                console.error('gRPC server error:', err);
                reject(err);
                return;
            }
            server.start();
            console.log(`gRPC server listening on port ${port}`);
            resolve();
        });
    });
};

export { startGrpcServer };

Let's break down what's happening here:

  1. We're importing the necessary gRPC libraries and the path module.
  2. We're defining the path to our .proto file.
  3. We're using protoLoader.loadSync to load the Protocol Buffer definition. The options we pass ensure that the generated code is compatible with gRPC.
  4. We're using grpc.loadPackageDefinition to load the gRPC service definition.
  5. We're defining the sayHello function, which is the implementation of our gRPC method. It takes a call object and a callback function. We extract the name from the request and return a greeting.
  6. We're creating a function startGrpcServer that starts the gRPC server. This function returns a Promise, similar to our startExpressServer function. This helps us manage the asynchronous nature of server startup and handle errors.
  7. Inside startGrpcServer, we create a new gRPC server instance, add our service, bind the server to a port, and start it.
  8. We log a message to the console when the server is successfully started and reject the promise if the server fails to start.

Now that we have both our Express and gRPC servers set up, we need to integrate them into a single process and handle restarts.

Integrating Servers and Handling Restarts

Now for the grand finale: integrating our Express and gRPC servers into a single process and implementing graceful restarts. This is where we'll tie everything together and ensure our application is resilient to crashes.

Create a new file named src/index.ts. This will be our main entry point for the application. Here's how we can integrate the servers and handle restarts:

import { startExpressServer } from './express-server';
import { startGrpcServer } from './grpc-server';

async function main() {
  try {
    await Promise.all([
      startExpressServer(),
      startGrpcServer()
    ]);
    console.log('Both servers started successfully!');
  } catch (error) {
    console.error('Failed to start one or more servers:', error);
    process.exit(1);
  }
}

main();

process.on('uncaughtException', (err) => {
  console.error('Uncaught exception:', err);
  // Perform any necessary cleanup here
  process.exit(1);
});

process.on('unhandledRejection', (err) => {
  console.error('Unhandled rejection:', err);
  // Perform any necessary cleanup here
  process.exit(1);
});

Let's break down what's happening in this file:

  1. We're importing the startExpressServer and startGrpcServer functions from our respective server files.
  2. We're creating an async function main that will start both servers concurrently using Promise.all. This ensures that both servers start at the same time.
  3. We're wrapping the server startup in a try...catch block to handle any errors that might occur during startup. If either server fails to start, we log the error and exit the process.
  4. We're calling the main function to start the application.
  5. We're adding global error handlers for uncaughtException and unhandledRejection. These handlers will catch any unhandled exceptions or promise rejections that occur in our application. When an error is caught, we log it, perform any necessary cleanup (you might want to add custom cleanup logic here, like closing database connections), and exit the process.

With this setup, if either the Express server or the gRPC server crashes due to an unhandled exception or promise rejection, the process will exit. This is where process managers like pm2 or Docker's restart policies come into play. These tools can automatically restart the process when it exits, ensuring that our servers are back up and running quickly.

To use pm2, you can install it globally:

npm install -g pm2

Then, you can start your application using pm2:

pm run build
pm2 start dist/index.js --name "multi-server-app"

pm2 will monitor your application and automatically restart it if it crashes. You can also use other process managers or container orchestration tools like Docker to achieve the same result.

Important Considerations:

  • Cleanup: In the error handlers, we've added placeholders for cleanup logic. In a real-world application, you'll want to add code to gracefully shut down your servers, close database connections, and perform any other necessary cleanup tasks before exiting the process. This will help prevent data loss and ensure a cleaner restart.
  • Logging: We're logging errors to the console, but in a production environment, you'll want to use a more robust logging solution. Tools like Winston or Bunyan can help you manage logs effectively.
  • Health Checks: Implementing health checks is crucial for monitoring the status of your servers. You can expose an endpoint on your Express server (e.g., /health) that returns a 200 OK status if the server is healthy. You can also implement health checks for your gRPC server. Process managers and orchestration tools can use these health checks to determine when to restart a server.

Conclusion

So there you have it! We've successfully set up an application that runs both an Express server and a gRPC server in a single process, with graceful restarts handled using global error handlers and a process manager like pm2. This approach can be a great way to optimize resource usage and simplify deployment, but it's important to handle errors and restarts carefully to ensure your application remains resilient.

Remember, this is just a starting point. In a real-world application, you'll want to add more robust error handling, logging, health checks, and cleanup logic. You might also want to explore more advanced techniques like circuit breakers and load balancing to further improve the resilience and scalability of your system. But with the foundation we've built here, you're well on your way to building robust and scalable microservices applications!