Advanced use case of morgan middleware in express

Here's a more complex use case for morgan in an Express.js application, where we customize the logging format and also log to a file using a rotating file stream for better management of logs:

1. Install Dependencies: You'll need morgan, rotating-file-stream, and fs (Node.js filesystem module) if not already installed:

   npm install morgan rotating-file-stream fs
   

2. Setting Up morgan with Rotating File Stream:

   const express = require('express');
   const morgan = require('morgan');
   const fs = require('fs');
   const path = require('path');
   const rfs = require('rotating-file-stream');
   
   const app = express();
   
   // Define log directory and create it if it doesn't exist
   const logDirectory = path.join(__dirname, 'log');
   fs.existsSync(logDirectory) || fs.mkdirSync(logDirectory);
   
   // Create a rotating write stream for log files
   const accessLogStream = rfs.createStream('access.log', {
       interval: '1d', // rotate daily
       path: logDirectory
   });
   
   // Define custom token for logging request processing time
   morgan.token('response-time-ms', function(req, res) {
       return `${res['response-time']}ms`;
   });
   
   // Use morgan middleware with custom format and stream
   app.use(morgan(':date[iso] :method :url :status :response-time-ms', { stream: accessLogStream }));
   
   // Example route
   app.get('/', (req, res) => {
       res.send('Hello World!');
   });
   
   // Start the server
   const PORT = process.env.PORT || 3000;
   app.listen(PORT, () => {
       console.log(`Server is running on http://localhost:${PORT}`);
   });
   

3. Explanation:

   • const rfs = require('rotating-file-stream');: This module provides a rotating file stream which automatically rotates log files based on size or date.
   • const accessLogStream = rfs.createStream('access.log', { options });: Creates a rotating file stream named access.log in the log directory. It rotates daily (interval: '1d') and stores logs in the specified logDirectory.
   • morgan.token('response-time-ms', function(req, res) { ... });: Defines a custom token response-time-ms to log the response time in milliseconds (res['response-time']).
   • app.use(morgan(':date[iso] :method :url :status :response-time-ms', { stream: accessLogStream }));: Uses morgan middleware with a custom logging format that includes the date in ISO format, HTTP method, URL, response status, and response time in milliseconds. It streams the log output to accessLogStream.

4. Running the Application:

   • When you run your Express application with this setup, morgan will log each request's details (HTTP method, URL, status, response time) to both the console and the access.log file in the log directory. The logs will be rotated daily as specified.

This setup is useful for production environments where logging needs to be more robust and organized across multiple files. It ensures that log files do not grow too large and are easier to manage over time. Adjust the configuration (interval, path, custom tokens) as per your application's logging requirements.