Wake On Demand (Load Balanced Solutions ?)

Question

I'm out of idea facing a challenging situation : Wake up a server on demand.

The problem

Wake-up a physical server that listen on specific port, when an incoming packet arrives. There may be a controller/middleware between clients and the server, but it should not affect bandwidth (and transparent for users).

The main goal : saving power consumption.

What I've tried

The setup I've tried for this demonstration is applied for a Samba NAS server.

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• preexec samba command (Automatic WoL remote filesystem, Transparent gateway for FileServer) : The goal of this solution is to expose a front NAS that accept all requests, and when a user want to access to a specific share, the preexec command will wake up the server with a custom script.

  preexec topology

  • PROS : Transparent for users in established state
  • CONS : Not generic, Bandwith affected

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• Firewall wake up : similar to the previous option, but acting at transport layer regarding to the requested port the firewall will wake up the server. Requires a subnet for masquerading the server.

  firewall topology

  • PROS : Generic, Transparent for users in established state
  • CONS : Bandwith affected, Requires a new subnet

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• IPVS DR : based on load-balanced environments, the goal is to take advantage of the floating IP address. I've imaginated to modify the ipvs stack (ipvsadm or keepalived) by implementing the wake-up server feature when a request arrives. That's a lot of works and searching, that's why I would prefer to see if there are another solutions ;)

  IPVS DR topology

  • PROS : Generic, Transparent for users in established state, Bandwith not affected
  • CONS : Hard to set up ?

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This is an example with the NAS server, but I would prefer an elegant and generic solution to solve this problem.

Any ideas ? :)

Answer 1

Possibly the easiest solution, fully transparent:

1. select a "WoL server": that can be a tiny creditcard computer, or a service on an already present machine - anything you can run a packet capture on and that can use a (more or less) dedicated NIC for capturing; possibly you could also use a router suitable for scripting
2. on the switch to the physical server, configure port mirroring from the physical server port to the WoL server port
3. on the WoL server, run a packet capture with an appropriate filter - ARP for the physical server IP, SYN for HTTP socket, ...
4. on the WoL server, run a small script monitoring the captured packets and on a hit, send a WoL packet to the physical server

Don't forget to add a static ARP entry on the upstream router if you're using a higher layer trigger frame like SYN for HTTP.