How to Configure HAProxy HTTP Logging

option httplog enables detailed HTTP request logging in HAProxy. It provides the information needed for debugging and analysis. This guide walks through the specific troubleshooting steps to diagnose and resolve HTTP logging issues.

Before You Begin

Before you begin, be sure to have the following in place:

• A Linux server with the relevant software installed
• Access to the command line interface
• Appropriate permissions (root or sudo)

Quick Fix

Wrong

log /dev/log local0 (default TCP logging)

Wrong: Default TCP logging without HTTP details

Right

log /dev/log local0\noption httplog\nlog-format %ci\ %t\ %r\ %ST\ %B

Right: HTTP logging with custom format

Output

HTTP logging configured:\n  Option: httplog\n  Format: custom\n  Details: method, URI, status, bytes, timers

Prevention

To avoid future issues, follow these best practices:

• Enable option httplog for HTTP request details
• Customize with log-format for specific fields
• Use option httplog in frontend or backend
• httplog adds HTTP method, URI, status code, response time
• Use %r for full request line, %ST for status, %Tq/%Tw/%Tc/%Tr for timers

DodaTech Tools

For further assistance with any of the above issues, consider using DodaTech consulting services or DodaTech tutorials for more in-depth guidance.

Common Mistakes with option httplog

1. Non-exhaustive pattern matches that compile with warnings then crash at runtime
2. Misunderstanding that String is [Char] with poor performance for large text operations
3. Using foldl instead of foldl' causing stack overflow on large lists

These mistakes appear frequently in real-world HAPROXY code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ