3003.md
root@localhost:~# cat 3003.md

Localhost:3003 Development Port

# 定义

Port 3003 emerged as a natural alternative to port 3000 in Node.js development ecosystems. When developers need to run multiple Node.js applications simultaneously, or when port 3000 is occupied by another service, port 3003 provides a logical next choice. It maintains the 3000-series pattern familiar to Node.js developers while providing enough separation to avoid conflicts. This port is particularly useful in microservices architectures and full-stack development environments.

# Services and Software That Use Port 3003

## Node.js Applications

• Express.js Secondary Server
Additional Express.js applications running when primary server uses port 3000.
• Node.js API Server
Backend API services that need to run alongside frontend development servers.
• Microservices
Individual microservice instances in a distributed Node.js architecture.
• Custom Node.js Scripts
Development scripts and utilities that require HTTP server functionality.

## Development Environments

• Full-Stack Development
Backend services running on 3003 while frontend uses 3000, enabling complete local development.
• Multi-Tenant Applications
Different application instances or tenant-specific services.
• A/B Testing Environments
Alternative versions of applications for comparison and testing.

## Testing & Development Tools

• Mock API Servers
Development mock servers that simulate production APIs for frontend testing.
• Webhook Receivers
Local webhook endpoints for testing third-party integrations.
• Development Proxies
Proxy servers for API routing and development traffic management.

## Other Tools

• Socket.io Servers
Real-time communication servers running separately from main application.
• File Upload Services
Dedicated file handling services in multi-service architectures.
• Background Job Servers
Task processing services with HTTP interfaces for monitoring.

# Frequently Asked Questions

Q: How do I access localhost:3003?

A:

Start your Node.js application configured for port 3003, then open http://localhost:3003 in your browser or use it as the base URL for API requests.

Q: When should I use port 3003 instead of 3000?

A:

Use port 3003 when port 3000 is occupied by another service, when running multiple Node.js applications simultaneously, or when separating frontend (3000) and backend (3003) services.

Q: How do I run multiple Node.js apps on different ports?

A:

Set different PORT environment variables for each app, use process managers like PM2, or configure each application's server to listen on specific ports (3000, 3001, 3002, 3003, etc.).

Q: How to fix CORS issues between localhost:3000 and localhost:3003?

A:

Configure your backend server (usually on 3003) to allow requests from localhost:3000 in CORS settings. Add the origin to your CORS whitelist or use middleware like cors in Express.js.

Q: How to set environment variables for port 3003?

A:

Set PORT=3003 in your environment, create a .env file with PORT=3003, or use npm scripts like "start:api": "PORT=3003 node server.js" for consistent configuration.

Q: Should I use port 3003 in production?

A:

Port 3003 is primarily for development. In production, use standard ports (80, 443) behind a reverse proxy, or let your hosting platform assign ports dynamically.

Q: How to manage multiple services on ports 3000 and 3003?

A:

Use tools like PM2, Docker Compose, or npm scripts with concurrently. Create clear documentation of which service runs on which port for team consistency.

Q: Why is my app starting on port 3000 instead of 3003?

A:

Check your PORT environment variable, application configuration, and npm scripts. Ensure you're not overriding the port setting elsewhere in your code or configuration files.

# How to Use Port 3003

1.

Check Port Availability

Verify that port 3003 is available and understand why you're not using port 3000 (conflict resolution).

bash
lsof -i :3003
2.

Configure Node.js Application

Set your Node.js application to listen on port 3003. This can be done via environment variables or direct configuration.

bash
PORT=3003 node server.js
3.

Start Your Application

Launch your Node.js application on port 3003. Ensure proper error handling for port conflicts.

bash
npm start -- --port 3003
4.

Verify Application Access

Test that your application is accessible on port 3003 and functioning correctly.

bash
curl http://localhost:3003
5.

Configure Development Workflow

Update your development scripts, environment files, and documentation to reflect the port 3003 configuration.

# Common Problems

## MEDIUM Severity Issues

⚠ Port 3003 Conflict with Port 3000

Confusion between applications running on port 3000 and 3003, leading to requests being sent to the wrong service.

⚠ Cross-Service Communication

Services running on different ports (3000, 3003) having trouble communicating due to hardcoded URLs or CORS issues.

⚠ Process Management Issues

Multiple Node.js processes running on different ports becoming difficult to track and manage.

## HIGH Severity Issues

⚠ Environment Variable Issues

Incorrect PORT environment variable configuration causing the application to start on the wrong port or fail to start.

## LOW Severity Issues

⚠ Development Tool Confusion

Development tools and browser bookmarks pointing to wrong ports, causing confusion during development.

# Troubleshooting Solutions

## All Platform

Fix Multi-Port Service Communication

For: Cross-Service Communication

Steps:

  1. Configure CORS settings to allow cross-origin requests between ports
  2. Use environment variables for service URLs instead of hardcoding
  3. Set up proper API base URLs for different environments
  4. Test communication between services on different ports
all
export API_BASE_URL=http://localhost:3003

Fix Multi-Port Service Communication

For: Cross-Service Communication

Steps:

  1. Configure CORS settings to allow cross-origin requests between ports
  2. Use environment variables for service URLs instead of hardcoding
  3. Set up proper API base URLs for different environments
  4. Test communication between services on different ports
all
curl -H "Origin: http://localhost:3000" http://localhost:3003/api/health

Manage Multiple Node.js Processes

For: Process Management Issues

Steps:

  1. Use process managers like PM2 for better control over multiple services
  2. Create npm scripts for starting services on specific ports
  3. Document port assignments for team development
  4. Use tools like concurrently for running multiple processes
all
npm install -g pm2

Manage Multiple Node.js Processes

For: Process Management Issues

Steps:

  1. Use process managers like PM2 for better control over multiple services
  2. Create npm scripts for starting services on specific ports
  3. Document port assignments for team development
  4. Use tools like concurrently for running multiple processes
all
pm2 start server.js --name api-server -- --port 3003

Manage Multiple Node.js Processes

For: Process Management Issues

Steps:

  1. Use process managers like PM2 for better control over multiple services
  2. Create npm scripts for starting services on specific ports
  3. Document port assignments for team development
  4. Use tools like concurrently for running multiple processes
all
npx concurrently "npm run dev" "npm run api --port=3003"

# Summary

root@localhost:~# echo "Port 3003 Documentation Complete"

What it is: localhost:3003 is Localhost:3003 is commonly used as an alternative Node.js development port when port 3000 is already occupied. It serves as a secondary development port for Node.js applications, microservices, API servers, and multi-service development environments where multiple Node.js processes need to run simultaneously.

Who uses it: Express.js Secondary Server, Node.js API Server, Microservices, Custom Node.js Scripts, Full-Stack Development, Multi-Tenant Applications, A/B Testing Environments, Mock API Servers, Webhook Receivers, Development Proxies, Socket.io Servers, File Upload Services, Background Job Servers

Access URL: http://localhost:3003