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Comment by nodesocket | Hacker News Reader

The downtime "gap" between step 1 and step 2 is probably way less than 500ms right? If being down for 500ms, is unacceptable, you probably should have multiple HAProxy instances running, and just do a rolling deploy. Seems like a bit of over-optimization.

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Exactly, with these "high uptime" requirements, isn't it usual to have 2+ HAProxy instances running on different servers bound to the same IP? At least that's how I do it. When you update the config, first update the backup HAProxy, then update the main one. Any requests that take place during the main proxy restart would go to the backup.

Could you please describe how can I bind 2 different servers to the same IP with automatic request balancing (so when one server is down, another one will serve all requests)? I understand how to do it with another server with HAProxy, but your solution seems to be without HAProxy.

Apologies for the delay. We do use HAProxy.

To have 2 servers with the same IP, we use VRRP (Virtual Router Redundancy Protocol) and keepalived. HAProxy is setup on 2 separate servers/instances, and using VRRP/keepalive they both share an IP address (which HAProxy binds to). The servers also have their own unique IP address(es) (on top of the shared one), so the shared address doesn't really "belong" to any machine.

If one server goes down, VRRP gives the IP to the other server and that HAProxy takes over.

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