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Comment by jsiepkes | Hacker News Reader

Looks really cool! Though a simpler solution for most people will probably be OpenBSD's CARP protocol to share a single virtual IP between multiple boxes (with for example relayd). ECMP routing can get complex fast.

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CARP and the likes rely on the presence of an L2 layer which means you get limited scale or increased risk of a global outage. An L3 design scales very well and is resilient (notably because of the distributed control plane and the inability to create a loop).

Also note that CARP, VRRP, HSRP, and GLBP are all layer 3 load balancing protocols (that rely on layer 2 magic to work) whereas this is a layer 4 load balancer. Meaning I can connect to a single IP and a single port (80) and get consistently and equitably load balanced to exactly one server (of many) at another IP address.

Or VRRP with the open source keepalived, which has been around for a decade+ and works wonderfully on Linux.

That is exactly what Stack Overflow uses: keepalived to manage a virtual IP between two decent sized baremetal HAProxy servers (w/ bonded 10G nics). Works great and combined with DNS or Anycast based load balancing can scale pretty damn well. Definitely worth investigating as a KISS approach. To quote a recent Atwood tweet:

"if I have learned anything in my career, it is the shocking effectiveness of building ... literally the stupidest thing that could work. (And then iterating on it for a decade.)"

https://twitter.com/codinghorror/status/1026332543153389569

Indeed! It powers all of the internal loadbalancing (non-direct customer facing) for ticketmaster.com. I was on the core systems team ~12 or so years ago and learned all about how great it is.

Unfortunately it is not an option on some cloud providers, because you don't get true layer 2.

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