Conditional logging in Nginx - Mini Project: Build & Apply

Conditional logging in nginx

📖 Scenario: You are managing a web server using nginx. You want to log only requests that have a status code of 400 or higher to keep your logs focused on errors and warnings.

🎯 Goal: Configure nginx to log only error requests (status code 400 and above) using conditional logging.

📋 What You'll Learn

Create a variable to check if the status code is 400 or higher

Use this variable to conditionally enable logging

Configure the access_log directive to use this conditional logging variable

Verify the configuration by printing the relevant nginx config lines

💡 Why This Matters

🌍 Real World

Web servers often generate large logs. Conditional logging helps focus on errors, saving disk space and making troubleshooting easier.

💼 Career

DevOps engineers and system administrators use conditional logging to optimize server monitoring and improve incident response.

1

Create a variable to detect error status codes

In the nginx configuration, create a variable called $log_errors that is set to 1 if the response status code is 400 or higher, otherwise 0. Use the map directive with $status to do this.

Nginx

# Your code here

Need a hint?

Use the map directive to assign 1 to $log_errors when $status starts with 4 or higher.

2

Add conditional logging using the variable

Add an access_log directive that uses the variable $log_errors to enable logging only when $log_errors is 1. Use the built-in main log format and set the log file path to /var/log/nginx/error_requests.log.

Nginx

map $status $log_errors {
    default 0;
    ~^[4-9] 1;
}

# Your code here

Need a hint?

Use access_log with the if= parameter to conditionally log requests.

3

Add a server block with the conditional logging

Create a server block listening on port 80 that includes the access_log directive with conditional logging using $log_errors. Inside the server block, add a simple location / that returns status 200 with the text OK.

Nginx

map $status $log_errors {
    default 0;
    ~^[4-9] 1;
}

access_log /var/log/nginx/error_requests.log main if=$log_errors;

# Your code here

Need a hint?

Wrap the access_log and location inside a server block listening on port 80.

4

Print the final nginx configuration

Print the entire nginx configuration you created so far to verify the conditional logging setup.

Nginx

map $status $log_errors {
    default 0;
    ~^[4-9] 1;
}

server {
    listen 80;
    access_log /var/log/nginx/error_requests.log main if=$log_errors;

    location / {
        return 200 'OK';
    }
}

# Print the nginx config below
# Your code here

Need a hint?

Use a print statement to output the full nginx configuration text exactly as written.