proxy_pass directive in Nginx - Commands & Configuration

Introduction

Sometimes you want your web server to forward requests to another server or service. The proxy_pass directive in nginx helps you do this by sending client requests to a different backend server.

When you want nginx to forward requests to a web application running on another server or port.

When you want to hide the real backend server from users for security or simplicity.

When you want to load balance requests between multiple backend servers.

When you want to serve static files from nginx but pass dynamic requests to an application server.

When you want to add caching or security features in front of your backend service.

Config File - nginx.conf

nginx.conf

events {}
http {
    server {
        listen 8080;

        location /app/ {
            proxy_pass http://localhost:5000/;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
        }
    }
}

This configuration sets up an nginx server listening on port 8080.

The location /app/ block tells nginx to forward all requests starting with /app/ to the backend server at http://localhost:5000/.

The proxy_set_header lines pass the original host and client IP to the backend server, which helps with logging and security.

Commands

This command tests the nginx configuration file for syntax errors before applying it.

Terminal

sudo nginx -t

Expected Output

nginx: the configuration file /etc/nginx/nginx.conf syntax is ok

nginx: configuration file /etc/nginx/nginx.conf test is successful

This command reloads nginx to apply the new configuration without stopping the server.

Terminal

sudo systemctl reload nginx

Expected Output

No output (command runs silently)

This command sends a request to nginx on port 8080 at path /app/ to verify that proxy_pass forwards the request to the backend server.

Terminal

curl -i http://localhost:8080/app/

Expected Output

HTTP/1.1 200 OK

Server: nginx/1.24.0

Date: Thu, 01 Jun 2024 12:00:00 GMT

Content-Type: text/html

Content-Length: 13



Hello from app

Key Concept

If you remember nothing else from this pattern, remember: proxy_pass forwards client requests from nginx to another server or service.

Common Mistakes

Not including a trailing slash at the end of the proxy_pass URL.

Without the trailing slash, nginx appends the full original request URI to the proxy_pass URL, which can cause incorrect backend paths.

Always include a trailing slash at the end of the proxy_pass URL if you want to replace the matching part of the request URI.

Forgetting to reload nginx after changing the configuration.

Changes won't take effect until nginx reloads the configuration, so the proxy_pass won't work as expected.

Run 'sudo nginx -t' to test and then 'sudo systemctl reload nginx' to apply changes.

Not setting proxy_set_header for Host and X-Real-IP.

The backend server may not receive the correct client IP or host information, causing logging or routing issues.

Add proxy_set_header directives to pass original client info to the backend.

Summary

Use proxy_pass in nginx to forward requests to another server or service.

Test your nginx configuration with 'nginx -t' before reloading.

Reload nginx to apply changes and verify with curl requests.

Practice

1. What is the primary purpose of the proxy_pass directive in an Nginx configuration?

easy

A. To block incoming requests based on IP address

B. To serve static files directly from Nginx

C. To forward client requests to another server

D. To rewrite URLs within the same server

Solution

1. Step 1: Understand the role of proxy_pass

   The proxy_pass directive is used to send client requests received by Nginx to another server, often called a backend or upstream server.

2. Step 2: Compare with other options

   Serving static files is done by root or alias, blocking IPs uses deny, and URL rewriting uses rewrite. These are different from proxy_pass.

3. Final Answer:

   To forward client requests to another server -> Option C

4. Quick Check:

   proxy_pass forwards requests [OK]

Hint: Remember: proxy_pass sends requests to another server [OK]

Common Mistakes:

• Confusing proxy_pass with static file serving
• Thinking proxy_pass blocks requests
• Mixing proxy_pass with URL rewriting

2. Which of the following is the correct syntax to forward all requests from /app/ to http://backend.local/ using proxy_pass inside a location /app/ block?

easy

A. proxy_pass http://backend.local/;

B. proxy_pass http://backend.local/app/;

C. proxy_pass backend.local;

D. proxy_pass http://backend.local

Solution

1. Step 1: Understand proxy_pass URL format

   The URL in proxy_pass must include the scheme (http://) and a trailing slash if you want to replace the matching part of the request URI.

2. Step 2: Analyze options

   proxy_pass http://backend.local/; uses http://backend.local/ with trailing slash, which correctly forwards requests replacing /app/ with /. proxy_pass http://backend.local/app/; appends /app/ again, causing duplication. proxy_pass backend.local; lacks scheme, invalid syntax. proxy_pass http://backend.local misses trailing slash, causing different URI handling.

3. Final Answer:

   proxy_pass http://backend.local/; -> Option A

4. Quick Check:

   Correct proxy_pass URL includes scheme and trailing slash [OK]

Hint: Always include scheme and trailing slash for correct URI mapping [OK]

Common Mistakes:

• Omitting http:// scheme
• Missing trailing slash causing URI errors
• Appending location path twice

3. Given this Nginx config snippet:

location /api/ {
    proxy_pass http://backend.local/;
}

If a client requests /api/users, what will be the proxied request URI sent to http://backend.local?

medium

A. /api/users

B. /users

C. /

D. /api/

Solution

1. Step 1: Understand URI replacement with trailing slash

   When proxy_pass URL ends with a slash, Nginx replaces the matching part of the request URI (/api/) with the path in proxy_pass (which is / here).

2. Step 2: Apply to example

   Request URI /api/users has /api/ replaced by /, resulting in /users sent to backend.

3. Final Answer:

   /users -> Option B

4. Quick Check:

   Trailing slash in proxy_pass replaces matching location path [OK]

Hint: Trailing slash means replace matching URI part [OK]

Common Mistakes:

• Assuming original URI is sent unchanged
• Confusing with proxy_pass without trailing slash
• Thinking /api/ prefix remains in proxied URI

4. You have this Nginx config:

location /service/ {
    proxy_pass http://backend.local/service/;
}

Clients report 404 errors from backend for requests like /service/data. What is the likely cause?

medium

A. proxy_pass URL duplicates the /service/ path causing wrong backend URI

B. Missing trailing slash in proxy_pass URL

C. Backend server is down

D. Nginx location block syntax error

Solution

1. Step 1: Analyze proxy_pass with matching location

   When proxy_pass URL includes the same path as location, Nginx appends the full request URI after it, causing duplication.

2. Step 2: Understand effect on backend URI

   Request /service/data becomes /service/service/data at backend, likely causing 404 errors.

3. Final Answer:

   proxy_pass URL duplicates the /service/ path causing wrong backend URI -> Option A

4. Quick Check:

   Duplicated path in proxy_pass causes 404 [OK]

Hint: Avoid repeating location path in proxy_pass URL [OK]

Common Mistakes:

• Ignoring duplicated path in proxy_pass
• Assuming backend down without checking URI
• Confusing missing slash with duplicated path

5. You want to forward requests from /app/ to http://backend.local/ but keep the original /app/ prefix in the proxied URI. Which proxy_pass configuration achieves this?

hard

A. proxy_pass http://backend.local/;

B. proxy_pass http://backend.local/app/

C. proxy_pass http://backend.local/app;

D. proxy_pass http://backend.local;

Solution

1. Step 1: Understand proxy_pass without trailing slash

   If proxy_pass URL has no trailing slash, Nginx appends the full original request URI after the host.

2. Step 2: Apply to example

   Using proxy_pass http://backend.local; inside location /app/ sends requests like /app/data as http://backend.local/app/data, preserving the prefix.

3. Final Answer:

   proxy_pass http://backend.local; -> Option D

4. Quick Check:

   No trailing slash keeps original URI prefix [OK]

Hint: No trailing slash keeps full original URI [OK]

Common Mistakes:

• Adding trailing slash removes original prefix
• Appending /app/ twice causing duplication
• Missing scheme in proxy_pass URL