example nginx config

nginx.conf

# This file routes requests for app1.example.com, app2.example.com, and app3.example.com
# to their corresponding backend services.
#
# Each application has two components:
# 1. A web server for the user interface (e.g., a Node.js/Express app serving HTML/CSS/JS).
# 2. A REST API server for data operations.

# Defines settings for HTTP traffic.
http {

    # Upstream groups define pools of backend servers. This makes the configuration
    # cleaner and allows for load balancing if you add more servers.

    # --- Upstream definitions for Application 1 ---
    upstream app1_web {
        # Server(s) for the browser-based UI of App 1
        server 127.0.0.1:3001;
    }
    upstream app1_api {
        # Server(s) for the REST API of App 1
        server 127.0.0.1:8001;
    }

    # --- Upstream definitions for Application 2 ---
    upstream app2_web {
        # Server(s) for the browser-based UI of App 2
        server 127.0.0.1:3002;
    }
    upstream app2_api {
        # Server(s) for the REST API of App 2
        server 127.0.0.1:8002;
    }

    # --- Upstream definitions for Application 3 ---
    upstream app3_web {
        # Server(s) for the browser-based UI of App 3
        server 127.0.0.1:3003;
    }
    upstream app3_api {
        # Server(s) for the REST API of App 3
        server 127.0.0.1:8003;
    }

    # Set common proxy headers in one place to avoid repetition.
    # These headers pass useful client information to the backend servers.
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;

    # =================================================================
    # Server Block for app1.example.com
    # =================================================================
    server {
        listen 80;
        server_name app1.example.com;

        # Location for the browser-based endpoint (e.g., the main website)
        location / {
            proxy_pass http://app1_web;
            # WebSockets support
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection 'upgrade';
        }

        # Location for the REST API endpoint
        # This matches any request starting with /api/
        location /api/ {
            # proxy_pass will forward the request to the API server.
            # The URI part (/api/) is passed along as well.
            proxy_pass http://app1_api;
        }
    }

    # =================================================================
    # Server Block for app2.example.com
    # =================================================================
    server {
        listen 80;
        server_name app2.example.com;

        location / {
            proxy_pass http://app2_web;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection 'upgrade';
        }

        location /api/ {
            proxy_pass http://app2_api;
        }
    }

    # =================================================================
    # Server Block for app3.example.com
    # =================================================================
    server {
        listen 80;
        server_name app3.example.com;

        location / {
            proxy_pass http://app3_web;
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection 'upgrade';
        }

        # Example of rewriting the URL before proxying.
        # This can be useful if your API server doesn't expect the /api prefix.
        location /api/ {
            rewrite /api/(.*) /$1 break; # Removes /api/ from the request URI
            proxy_pass http://app3_api;
        }
    }

    # A default server to catch requests that don't match any other server_name
    server {
        listen 80 default_server;
        server_name _; # Underscore is a catch-all server name

        location / {
            return 404; # Or return a specific error page
        }
    }
}

# The 'events' block is required but can be empty for basic configurations.
events {
    worker_connections 1024;
}