[erlang-questions] clarify: gen_udp Set outbound ip address

[Decker, Nils]

Hello

> Von: erlang-questions-bounces@REDACTED 
> [mailto:erlang-questions-bounces@REDACTED] Im Auftrag von mog
> [...]
> reliability.  So I really need a way to have a cloud of computers
> running under one ip.  I imagine i could use a mirrored 
> switch and then
> forge the udp packets, but I was trying to do this without any custom
> hardware.  Has anyone developed a system like this? and If not how did
> you reach such high levels of reliability.

I did some research into this. There is a CLUSTERIP target in the linux iptables firewall that gives all nodes in a cluster the same MAC address and accepts connections based on a hash of ip/srcport/dstport. You can change dynamically which node serves which hash numbers. So if a node leaves the cluster some other node can pick up its hash value.
This will invalidate all open tcp sessions but the cluster is still reachable without delay. You need to have all nodes on a single hub. (you could configure a redundant switch to act as a hub...)

Because i dont have control over the switch, i implemented something else. I have one distributed application that owns the cluster ip address. It will bring up/down the ip on its node. The drawback is that i have to wait for the router refresh its arp cache.

Greetings
  Nils Decker

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