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The solution you mention has some tradeoffs. Imagine that you have hundreds of services each of which have a port and have some long running connections. With y

The solution you mention has some tradeoffs. Imagine that you have hundreds of services each of which have a port and have some long running connections. With your solution you can only restart the load balancer at the rate of the longest running connections or whenever ports run out, whichever comes first. Also then you'd have to maintain the logic to do the port mapping, iptables switching, draining, etc ... The post mentions they considered this option and they claim that they were worried about engineering risk; seems reasonable to be worried about that.

moe 12y ago
With your solution you can only restart the load balancer at the rate of the longest running connections Well, perhaps I should have provided more detail. Our ansible deployment script actually counts the port up until it finds a free one (we keep a port-range reserved for this purpose). So if there are multiple changes in rapid succession then more than two haproxy instances may dangle around for a while. The "port discovery" is a shell-task that registers the port to be used as a variable, which is then used by the templates of the haproxy and iptables roles. The cleanup is done by a 15min-cronjob which kills all haproxy instances that have no connections in netstat and don't match the haproxy pidfile.