How to Configure HAProxy Load Balancing Algorithms

The balance algorithm determines how traffic is distributed among backend servers. Choosing the right algorithm is critical for application performance. This guide walks through the specific troubleshooting steps to diagnose and resolve balance algorithm 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

balance roundrobin (default, may not suit all apps)

Wrong: Default roundrobin for long-lived connections

Right

backend app\n    balance leastconn\n    server app1 10.0.0.1:8080 check\n    server app2 10.0.0.2:8080 check

Right: leastconn for applications with varying request durations

Output

Balance algorithm: leastconn\nNew connections go to server with fewest active connections

Prevention

To avoid future issues, follow these best practices:

• Use roundrobin for short-lived HTTP requests
• Use leastconn for long-lived connections (WebSockets, APIs)
• Use source for IP-based persistence (no cookies needed)
• Use uri for cache-optimized routing
• Use first to minimize active server count

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 balance

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