Nginx Log DNS Resolver

nginx-logresolver is a Bash script that processes Nginx access logs and resolves IP addresses to hostnames in real time. It improves the readability of logs by replacing IPs with their corresponding hostnames using system DNS resolution. The script optionally colorizes the output and checks if dnsmasq is installed to improve performance via local DNS caching.

Why?

By default, Nginx logs contain raw IP addresses instead of hostnames. This is intentional: resolving hostnames requires DNS lookups, which are relatively slow and can degrade performance under high traffic.

However, hostnames can be helpful for:

• Identify traffic from known domains or bots
• Spot patterns in abuse or suspicious activity
• Debug or audit logs with more context

This script reads logs after they are written, performing DNS resolution on-the-fly without changing Nginx’s configuration or degrading its performance.

Features

• Resolves IP addresses to hostnames in real time as logs are written.
• Checks if dnsmasq is installed and suggests using it for faster local DNS caching.
• Optional colored output via the -c / --color flag (requires grc).
• Skips confirmation prompts using the -y / --yes flag.
• Lightweight and minimal — pure Bash with no caching layer.

Requirements

• bash
• getent for DNS resolution
• grc (optional, for colored output)
• tail
• Access to your Nginx logs (default: /var/log/nginx/access.log — can be customized)

Installation

git clone https://github.com/spithash/nginx-logresolver.git
cd nginx-logresolver
chmod +x nginx-logresolver.sh

Usage

Basic usage:

./nginx-logresolver.sh

With colorized output (requires grc):

./nginx-logresolver.sh -c

Skip dnsmasq warning:

./nginx-logresolver.sh -y

What It Does

• Tails logs in real time: Watches /var/log/nginx/access.log and processes new entries as they appear.
• Resolves IPs to hostnames: Uses getent hosts to replace the IP address in each log line with its corresponding hostname.
• Suggests dnsmasq: If dnsmasq is not found in common system paths, warns the user that enabling it will improve performance by caching DNS queries.
• Adds color: If -c is specified and grc is installed, applies syntax highlighting to logs using grc.

Example Output

host.example.com - - [07/May/2025:10:42:31 +0000] "GET /index.html HTTP/1.1" 200 1024 "-" "Mozilla/5.0"