[llama052]

I thought best practice for HAproxy was to run two HAProxy's in parallel with VRRP or DNS load balancing?

Does that not achieve the same outcome? I've used HAProxy for layer 4 in the past without any issue this way.

[gbrayut]

It does but that setup runs into limits on throughput of individual servers, and doesn't have the same drain/fill/failover capabilities discussed in the article.

To be clear, the HAProxy+vrrp+dns is often a better solution, but this describes an interesting design for a load balancing system that can handle many orders of magnitude more traffic and have maintenance without breaking established connections (one of it's core design features)

[wmf]

Imagine if you need a lot more than two HAProxies and they aren't in the same rack/subnet; that's where more sophisticated techniques come in.