IP-based access control (allow/deny) in Nginx - Mini Project: Build & Apply

IP-based access control (allow/deny) with nginx

📖 Scenario: You are managing a web server that should only allow access to certain trusted IP addresses. You want to configure nginx to allow or deny access based on client IPs.

🎯 Goal: Build an nginx configuration that allows access only from specific IP addresses and denies all others.

📋 What You'll Learn

Create a basic nginx server block configuration

Add a variable to hold the trusted IP address

Use allow and deny directives to control access

Print the final nginx configuration to verify the setup

💡 Why This Matters

🌍 Real World

IP-based access control is commonly used to restrict access to internal tools, admin panels, or sensitive web resources to trusted networks or IP addresses.

💼 Career

Understanding how to configure nginx for IP-based access control is a valuable skill for DevOps engineers and system administrators managing secure web servers.

1

Create a basic nginx server block

Create a variable called nginx_config that contains a basic nginx server block listening on port 80 with a root directory /var/www/html.

Nginx

# Create a variable called nginx_config with a basic server block
# Your code here

Hint

Use triple quotes to create a multi-line string for the nginx configuration.

2

Add a trusted IP variable

Add a variable called trusted_ip and set it to the string 192.168.1.100.

Nginx

nginx_config = '''server {
    listen 80;
    root /var/www/html;
}'''
# Add a variable called trusted_ip with value '192.168.1.100'
# Your code here

Hint

Use single quotes to assign the IP address string.

3

Add allow and deny directives

Update the nginx_config variable to include allow directive for the trusted_ip and a deny all; directive inside the server block.

Nginx

nginx_config = '''server {
    listen 80;
    root /var/www/html;
}'''
trusted_ip = '192.168.1.100'
# Update nginx_config to add allow and deny directives
# Your code here

Hint

Use an f-string to insert the trusted_ip variable inside the nginx configuration.

4

Print the final nginx configuration

Write a print statement to display the nginx_config variable.

Nginx

trusted_ip = '192.168.1.100'
nginx_config = f'''server {{
    listen 80;
    root /var/www/html;
    allow {trusted_ip};
    deny all;
}}'''
# Print the nginx_config variable
# Your code here

Hint

Use print(nginx_config) to show the configuration.

Practice

1. What does the allow directive do in an nginx configuration?

easy

A. It permits access to specified IP addresses or ranges.

B. It blocks access to specified IP addresses or ranges.

C. It redirects users to another URL.

D. It logs the IP addresses of visitors.

Solution

1. Step 1: Understand the purpose of allow

   The allow directive in nginx is used to specify which IP addresses or ranges are permitted to access the server or location.

2. Step 2: Compare with other directives

   Unlike deny which blocks IPs, allow explicitly permits them.

3. Final Answer:

   It permits access to specified IP addresses or ranges. -> Option A

4. Quick Check:

   allow means permit access [OK]

Hint: Allow means permit access, deny means block access [OK]

Common Mistakes:

• Confusing allow with deny
• Thinking allow redirects users
• Assuming allow logs IPs

2. Which of the following is the correct syntax to deny access to IP 192.168.1.10 in nginx?

easy

A. allow 192.168.1.10;

B. deny 192.168.1.10;

C. block 192.168.1.10;

D. reject 192.168.1.10;

Solution

1. Step 1: Identify the correct directive for blocking IPs

   In nginx, the directive to block or deny access is deny.

2. Step 2: Check syntax correctness

   The correct syntax is deny IP_address; with a semicolon at the end.

3. Final Answer:

   deny 192.168.1.10; -> Option B

4. Quick Check:

   deny blocks IP = deny 192.168.1.10; [OK]

Hint: Use 'deny IP;' to block access in nginx [OK]

Common Mistakes:

• Using 'allow' instead of 'deny'
• Using invalid directives like 'block' or 'reject'
• Missing semicolon at the end

3. Given this nginx config snippet inside a location /admin block:

allow 10.0.0.0/24;
deny all;

What happens when a user with IP 10.0.0.15 tries to access /admin?

medium

A. Access is denied because the IP is not explicitly allowed.

B. Access is denied because deny all overrides allow.

C. Access is allowed only if the user has a valid cookie.

D. Access is allowed because the IP is in the allowed range.

Solution

1. Step 1: Understand the order of allow and deny

   nginx checks allow and deny rules in order. If an IP matches an allow rule, access is granted even if deny all follows.

2. Step 2: Check if IP matches allowed range

   IP 10.0.0.15 is inside 10.0.0.0/24, so it matches the allow rule.

3. Final Answer:

   Access is allowed because the IP is in the allowed range. -> Option D

4. Quick Check:

   Allow matched before deny all = access allowed [OK]

Hint: Allow rules take priority before deny all [OK]

Common Mistakes:

• Assuming deny all always blocks
• Ignoring IP range matching
• Thinking cookies affect IP access control

4. You wrote this nginx config inside a server block:

deny 192.168.0.0/16
allow all;

But all IPs are denied access. What is the problem?

medium

A. You need to reload nginx after changes.

B. The order of deny and allow is wrong; allow should come first.

C. Missing semicolon after deny directive causes config error.

D. The IP range 192.168.0.0/16 is invalid.

Solution

1. Step 1: Check syntax for missing semicolons

   nginx requires semicolons at the end of each directive. The deny line is missing a semicolon, causing the config to fail.

2. Step 2: Understand effect of syntax error

   Without proper syntax, nginx may ignore or misinterpret rules, leading to unexpected blocking of all IPs.

3. Final Answer:

   Missing semicolon after deny directive causes config error. -> Option C

4. Quick Check:

   Every directive needs semicolon [OK]

Hint: Always end nginx directives with semicolon [OK]

Common Mistakes:

• Ignoring missing semicolon errors
• Thinking order alone causes issue
• Assuming IP range is invalid

5. You want to allow access only from IP 203.0.113.5 and block everyone else for /secure location. Which nginx config snippet achieves this correctly?

hard

A. location /secure {
allow 203.0.113.5;
deny all;
}

B. location /secure {
deny all;
allow 203.0.113.5;
}

C. location /secure {
allow all;
deny 203.0.113.5;
}

D. location /secure {
deny 203.0.113.5;
allow all;
}

Solution

1. Step 1: Understand correct order of allow and deny

   nginx processes allow and deny in order. To allow one IP and block others, allow must come first, then deny all.

2. Step 2: Verify each option

   location /secure {
     allow 203.0.113.5;
     deny all;
   }

   correctly allows 203.0.113.5 then denies all others.

   location /secure {
     deny all;
     allow 203.0.113.5;
   }

   denies all first, so no one is allowed. Options A and D misuse allow and deny directives.

3. Final Answer:

   location /secure { allow 203.0.113.5; deny all; } -> Option A

4. Quick Check:

   Allow specific IP then deny all others [OK]

Hint: Allow first, then deny all to restrict access [OK]

Common Mistakes:

• Reversing allow and deny order
• Allowing all then denying one IP
• Misusing deny and allow directives