[leetrout]

The biggest difference a few years ago was HA Proxy could do layer 4 load balancing where nginx was layer 7.

These days I think they’ve grown a lot closer together on capabilities. nginx remains a true web server where HA Proxy is not.

[wtarreau]

I'm not sure what you mean. HAProxy has always been a layer 4/7 load balancer and has indeed never been a web server.

NGINX historically was a web server (an excellent one) which has evolved towards proxying and a bit of load balancing. But in terms of LB features it lacks a lot, just like you wouldn't try to cross-dress haproxy into a web server in any way. It's true that for many quite simple setups nginx is often enough and saves the admin from having to learn another tool. But when you start to handle tens of thousands of domains, need to perform DDoS protection, handle thousands of servers, perform inter-DC state synchronization , stream tens of Gbps of traffic, or perform advanced actions on health check status change, it's not well suited aanymore. It's still the best web server I know, and many hosting infrastructures combine haproxy+varnish+nginx together, taking the best of each and deliver unrivaled quality of service. The beauty here is that these 3 best components in their respective categories are all free to use so there's no reason to have to choose between one or the other, just use all 3 and be happy!

[minxomat]

Nginx is a network tool with web server capabilities. It can also do pretty much everything you want as long as it's ipv4 or ipv6 over TCP, UDP or HTTP as it, and specifically the openresty distribution are highly scriptable. For example, a recent use case I solved with it was using it as a DNS (53 and DoT) proxy which also provided DoH and filtering.

For more use cases look at Kong, which is almost completely built on openresty.