1. Configuration Language: Fabio uses a simple configuration language based on key-value pairs that make it relatively easy to set up and manage, while HAProxy uses a more complex configuration language with a wide range of configuration options and parameters, providing granular control but requiring more expertise to configure.
2. Routing Methods: Fabio uses a service-based routing approach, where routing decisions are made based on service metadata like service name, version, and tags. In contrast, HAProxy relies on Layer 4 (TCP/UDP) and Layer 7 (HTTP) routing methods, allowing for more advanced routing strategies based on IP addresses, ports, and HTTP request attributes.
3. Load Balancing Algorithms: Fabio supports basic load balancing algorithms such as round-robin and random, whereas HAProxy offers a wider range of load balancing algorithms including least connections, source IP hash, and several others, allowing for more advanced traffic distribution strategies.
4. High Availability: HAProxy provides high availability features like active-passive and active-active setup using features like keepalived and VRRP, making it suitable for mission-critical applications requiring continuous operation even in case of failures. Fabio, on the other hand, lacks built-in high availability features, making it less suitable for environments where high uptime is a priority.
5. Logging and Monitoring: HAProxy offers robust logging and monitoring capabilities, allowing real-time insight into traffic patterns, performance metrics, and request/response details through integration with tools like Prometheus and Grafana. Fabio lacks advanced logging and monitoring features, limiting visibility into the system's operation and performance metrics.
6. SSL Offloading: HAProxy supports SSL termination and offloading, allowing the decryption of SSL/TLS traffic at the load balancer before forwarding it to backend servers, reducing the computational load on backend servers. Fabio lacks native support for SSL offloading, requiring additional configurations or components to handle SSL termination effectively.

In Summary, Fabio and HAProxy differ in aspects such as configuration language, routing methods, load balancing algorithms, high availability features, logging and monitoring capabilities, and SSL offloading support.