1. Scalability: AWS Elastic Load Balancing (ELB) offers scalable load balancing capabilities by automatically distributing incoming application traffic across multiple targets such as Amazon EC2 instances. In contrast, Fly uses a global network of servers for load balancing, allowing for high scalability and efficient traffic distribution. HAProxy is a software-based load balancer that can be scaled horizontally by adding more instances or vertically by upgrading hardware resources.

2. Cost: ELB pricing in AWS is usage-based and can vary depending on the amount of data processed and the type of resources used. Fly offers a pay-as-you-go pricing model that charges based on the number of requests served and the network egress traffic. HAProxy is an open-source solution, saving costs on licensing fees, but it requires more resources to manage and maintain in comparison to managed load balancers like ELB and Fly.

3. Features: ELB provides features like SSL termination, health checks, access logs, and content-based routing for managing traffic efficiently. Fly offers advanced features like global load balancing, automatic failover, multi-cloud support, and edge computing capabilities. HAProxy, being a software-based solution, provides flexibility in configuration and customization, allowing users to fine-tune load balancing behavior based on specific requirements.

4. Integration: ELB seamlessly integrates with other AWS services like Auto Scaling, Route 53, and CloudWatch for automated scaling and monitoring. Fly can be integrated with various cloud providers, CDNs, and deployment tools through APIs and plugins, enabling a flexible and interoperable infrastructure. HAProxy can be deployed on-premises or in the cloud and easily integrates with container orchestration platforms like Docker and Kubernetes for modern application deployments.

5. Performance: ELB is a managed service that offers high availability and low latency through intelligent traffic routing and load balancing algorithms. Fly uses anycast routing to optimize performance by directing traffic to the nearest server location, reducing latency and improving response times. HAProxy is known for its high performance and low overhead, capable of handling millions of connections per second with minimal impact on server resources.

6. Security: ELB provides built-in DDoS protection, SSL termination, and encryption for securing traffic between clients and servers. Fly ensures security through TLS encryption, access control lists, and firewall rules to protect against malicious attacks and data breaches. HAProxy offers security features like SSL offloading, client IP address preservation, and rate limiting to safeguard applications from potential threats and vulnerabilities.

In Summary, AWS Elastic Load Balancing, Fly, and HAProxy differ in terms of scalability, cost, features, integration, performance, and security, providing unique solutions for load balancing requirements in various environments.