Web server vs application server in Nginx - Visual Side-by-Side Comparison

Process Flow - Web server vs application server

Client sends HTTP request

↓

Web Server receives request

↓

Static content

↓

Serve file

↓

Application Server processes

↓

Response sent back to Web Server

↓

Web Server sends response to Client

The client sends a request to the web server. The web server serves static files directly or forwards dynamic requests to the application server, which processes them and returns a response.

Execution Sample

Nginx

server {
  listen 80;
  location / {
    root /var/www/html;
    index index.html;
  }
  location /app/ {
    proxy_pass http://localhost:8080;
  }
}

Nginx configuration serving static files from /var/www/html and forwarding /app/ requests to an application server on port 8080.

Process Table

Step	Request URL	Web Server Action	Application Server Action	Response Sent
1	/index.html	Serve static file /var/www/html/index.html	N/A	Static HTML content
2	/app/data	Forward request to app server at localhost:8080	Process dynamic request, generate JSON	JSON response
3	/about.html	Serve static file /var/www/html/about.html	N/A	Static HTML content
4	/app/login	Forward request to app server at localhost:8080	Process login, generate session token	Session token response
5	/favicon.ico	Serve static file /var/www/html/favicon.ico	N/A	Icon file content

💡 All requests handled either by serving static files or forwarding to application server for dynamic content.

Status Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
Request URL	N/A	/index.html	/app/data	/about.html	/app/login	/favicon.ico
Web Server Action	N/A	Serve static file	Forward to app server	Serve static file	Forward to app server	Serve static file
Application Server Action	N/A	N/A	Process dynamic request	N/A	Process login	N/A
Response Sent	N/A	Static HTML	JSON response	Static HTML	Session token	Icon file

Key Moments - 3 Insights

Why does the web server forward some requests to the application server?

Because those requests need dynamic processing which the web server alone cannot do, as shown in execution_table rows 2 and 4.

Can the web server serve dynamic content by itself?

No, the web server serves static files directly but forwards dynamic requests to the application server, as seen in the execution_table where only static URLs are served directly.

What happens if a request is for a static file?

The web server serves the file directly without involving the application server, as shown in execution_table rows 1, 3, and 5.

Visual Quiz - 3 Questions

Look at the execution table, what action does the web server take for the request '/app/data'?

A Serve static file

B Forward request to application server

C Return 404 error

D Cache the response

💡 Hint

Check the 'Web Server Action' column for step 2 in the execution_table.

At which step does the application server generate a session token?

A Step 4

B Step 3

C Step 1

D Step 5

💡 Hint

Look at the 'Application Server Action' column for step 4 in the execution_table.

If the web server did not forward '/app/login' requests, what would happen?

A Static login page would be served

B Application server would still process the request

C Request would fail or return an error

D Request would be cached

💡 Hint

Refer to the concept_flow and execution_table showing forwarding is needed for dynamic content.

Concept Snapshot

Web server handles HTTP requests.
Serves static files directly.
Forwards dynamic requests to application server.
Application server processes logic and returns response.
Nginx example: static content served from root, dynamic proxied to app server.

Full Transcript

When a client sends a request, the web server first checks if it is for static content like HTML or images. If yes, it serves the file directly. If the request is for dynamic content, such as data or login, the web server forwards it to the application server. The application server processes the request, runs any needed code, and sends back a response. The web server then sends this response to the client. This separation helps handle static and dynamic content efficiently.

Practice

1. What is the primary role of a web server like nginx?

easy

A. To deliver static files like images and HTML directly to users

B. To execute backend application logic and generate dynamic content

C. To store user data and manage databases

D. To compile source code into executable programs

Solution

1. Step 1: Understand the role of a web server

   A web server mainly serves static content such as images, HTML, CSS, and JavaScript files directly to users.

2. Step 2: Differentiate from application server

   An application server runs backend code to create dynamic content, which is different from a web server's role.

3. Final Answer:

   To deliver static files like images and HTML directly to users -> Option A

4. Quick Check:

   Web server = static file delivery [OK]

Hint: Web servers serve files; app servers run code [OK]

Common Mistakes:

• Confusing web server with application server
• Thinking web server runs backend logic
• Assuming web server manages databases

2. Which nginx configuration snippet correctly forwards requests to an application server on port 3000?

easy

A. location / { root http://localhost:3000; }

B. location / { fastcgi_pass http://localhost:3000; }

C. location / { proxy_pass http://localhost:3000; }

D. location / { redirect http://localhost:3000; }

Solution

1. Step 1: Identify correct directive for forwarding

   The proxy_pass directive is used in nginx to forward requests to an application server.

2. Step 2: Check other options for correctness

   root serves static files, fastcgi_pass is for FastCGI servers, and redirect sends HTTP redirects, not proxying.

3. Final Answer:

   location / { proxy_pass http://localhost:3000; } -> Option C

4. Quick Check:

   Use proxy_pass to forward requests [OK]

Hint: proxy_pass forwards; root serves static files [OK]

Common Mistakes:

• Using root instead of proxy_pass for forwarding
• Confusing fastcgi_pass with proxy_pass
• Using redirect which changes URL instead of proxying

3. Given this nginx config snippet, what happens when a user requests /app?

location /app {
  proxy_pass http://127.0.0.1:8080;
}

medium

A. nginx serves static files from /app directory

B. nginx forwards the request to the application server at 127.0.0.1:8080

C. nginx returns a 404 error

D. nginx redirects the user to http://127.0.0.1:8080/app

Solution

1. Step 1: Analyze the proxy_pass directive

   The proxy_pass directive tells nginx to forward matching requests to the specified backend server.

2. Step 2: Understand request handling

   Requests to /app are sent to the application server at 127.0.0.1:8080, not served as static files or redirected.

3. Final Answer:

   nginx forwards the request to the application server at 127.0.0.1:8080 -> Option B

4. Quick Check:

   proxy_pass forwards requests to backend [OK]

Hint: proxy_pass means forward, not serve or redirect [OK]

Common Mistakes:

• Thinking nginx serves static files here
• Confusing proxy_pass with redirect
• Assuming 404 error without backend

4. You configured nginx to forward requests to an application server using:

location /api {
  proxy_pass http://localhost:5000/api;
}

But requests to /api/users fail. What is the likely problem?

medium

A. nginx cannot forward requests to localhost

B. The location block should be location /api/ with trailing slash

C. proxy_pass must use HTTPS instead of HTTP

D. proxy_pass should be http://localhost:5000/ without /api

Solution

1. Step 1: Understand proxy_pass URI behavior

   When proxy_pass includes a URI (like /api), nginx replaces the matching part of the request URI with that URI, causing duplication.

2. Step 2: Correct proxy_pass to avoid URI duplication

   Removing /api from proxy_pass (using http://localhost:5000/) forwards the full original URI correctly.

3. Final Answer:

   proxy_pass should be http://localhost:5000/ without /api -> Option D

4. Quick Check:

   proxy_pass URI affects request path [OK]

Hint: Avoid URI in proxy_pass to prevent path duplication [OK]

Common Mistakes:

• Including URI in proxy_pass causing double paths
• Thinking HTTPS is required for localhost
• Believing nginx can't proxy localhost

5. You want nginx to serve static files from /var/www/html and forward API requests to an application server on port 4000. Which configuration correctly achieves this?

hard

A. location / { root /var/www/html; } location /api/ { proxy_pass http://localhost:4000/; }

B. location / { proxy_pass http://localhost:4000/; } location /api/ { root /var/www/html; }

C. location /api/ { root /var/www/html; } location / { proxy_pass http://localhost:4000/; }

D. location /api/ { proxy_pass http://localhost:4000/api/; } location / { root /var/www/html; }

Solution

1. Step 1: Assign root for static files

   The root directive in location / serves static files from /var/www/html.

2. Step 2: Forward API requests correctly

   The location /api/ block uses proxy_pass to forward API calls to the application server on port 4000.

3. Step 3: Verify order and correctness

   Static files served at root, API forwarded properly. Other options mix these roles incorrectly.

4. Final Answer:

   location / { root /var/www/html; } location /api/ { proxy_pass http://localhost:4000/; } -> Option A

5. Quick Check:

   Static files root + API proxy_pass = correct setup [OK]

Hint: Serve static at / root, proxy API at /api/ [OK]

Common Mistakes:

• Swapping root and proxy_pass locations
• Adding URI in proxy_pass causing path issues
• Not using trailing slash in location /api/