Software load balancers run on standard servers. HAProxy, NGINX, and Envoy are popular open-source options.
Advantages:
- Low cost: Free software on commodity hardware
- Elastic: Spin up more instances as needed
- Programmable: Modify routing logic in code
Disadvantages:
- You manage the infrastructure
- May need multiple instances for high availability
- Performance depends on underlying hardware
Cloud providers offer managed software balancers: AWS ELB/ALB, Google Cloud Load Balancer, Azure Load Balancer. You get software flexibility with managed operations.