Request body handling in Nginx - Mini Project: Build & Apply

Request Body Handling in Nginx

📖 Scenario: You are setting up an Nginx server to handle HTTP POST requests with JSON data. You want to configure Nginx to read the request body and store it in a variable for further processing or logging.

🎯 Goal: Configure Nginx to read the request body into a variable and then log the content of the request body.

📋 What You'll Learn

Create a server block with a location to accept POST requests

Add a directive to read the request body into a variable

Use the variable to log the request body content

Print the request body content in the access log

💡 Why This Matters

🌍 Real World

Many web applications need to inspect or log the content of POST requests for debugging, auditing, or routing decisions. Nginx can be configured to read and handle request bodies efficiently.

💼 Career

Understanding how to handle request bodies in Nginx is useful for DevOps engineers and site reliability engineers who manage web servers and need to troubleshoot or customize request processing.

1

Create a basic server block

Create an Nginx server block listening on port 8080 with a /post location that accepts POST requests.

Nginx

server {
    listen 8080;
    # Your code here
}

Need a hint?

Use server {} block with listen 8080; and a location /post {} inside.

2

Add directive to read request body

Inside the location /post, add the directive client_body_buffer_size 10k; and set client_body_in_file_only off; to enable reading the request body into memory.

Nginx

server {
    listen 8080;
    location /post {
        # Add client_body_buffer_size and client_body_in_file_only directives here
    }
}

Need a hint?

Use client_body_buffer_size 10k; to set buffer size and client_body_in_file_only off; to keep body in memory.

3

Capture request body into a variable

Inside the location /post, add the directive set $req_body ""; to initialize a variable, then use access_by_lua_block to read the request body into $req_body variable using Lua scripting.

Nginx

server {
    listen 8080;
    location /post {
        client_body_buffer_size 10k;
        client_body_in_file_only off;
        # Initialize $req_body variable
        # Use access_by_lua_block to read request body
    }
}

Need a hint?

Use set $req_body ""; to declare the variable and Lua code inside access_by_lua_block to read the body.

4

Log the request body content

Add a log_format named with_body that logs the $req_body variable, then set access_log to use this format inside the server block. Finally, add return 200 'OK'; inside the location /post to respond.

Nginx

log_format with_body '$remote_addr - $remote_user [$time_local] "$request" $status $body_bytes_sent "$http_referer" "$http_user_agent" "$req_body";  

server {
    listen 8080;
    access_log /var/log/nginx/access.log with_body;
    location /post {
        client_body_buffer_size 10k;
        client_body_in_file_only off;
        set $req_body "";
        access_by_lua_block {
            ngx.req.read_body()
            local data = ngx.req.get_body_data()
            if data then
                ngx.var.req_body = data
            end
        }
        # Add return statement here
    }
}

Need a hint?

Define log_format with $req_body, set access_log to use it, and add return 200 'OK'; in location.