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I am currently providing some web applications to my customers (apache/php/mysql on Windows server). I'm looking to provide some sort of fail-over server in the case my server has a hardware failure. My server is running in a data center.

I think I will just add a second server that is installed in the same rack. My 1st server will act as a spare server and I will add extra NICs to create a local network between the two servers. I will use mysql replication and something like rsync to synchronize all web applications continuously. Then I will set up some monitoring on the spare server so when my main server doesn't respond the spare server will change it's ip address to match the main one. (maybe a manual change instead of automatic).

My question is: Will changing the ip address make the transition almost instantly? Or will the router/switch in the data center not detect the change quickly enough (because of ARP caching). Do I also need to clone the MAC address in such a situation?

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help.ubuntu.com/community/HighlyAvailableLAMP for ubuntu/Deb but could easily be adapted for your flavor –  dc5553 Apr 27 '12 at 14:56

2 Answers 2

I don't think ARP caching will be a problem here.

However, I would be concerned with problems such as a partial failure of the main server (i.e. it doesn't respond to your monitoring requests but its network connection is still alive). If the monitoring triggers, you have to make sure the main server is offline (e.g. by switching it off using a switched PDU or by shutting down the switch port the server is connected to).

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Yes, it will probably be better to check it manually. And then really make sure the server is turned off. Also before booting it again it will probably help to make sure there won't be an ip address conflict. –  Ronald Apr 27 '12 at 14:59

It seems that you are implementing your own high availability solution. Why not just using an already available and reliable solution such as keepalived or heartbeat?

When using such a solution, you don't need to worry about ARP caching. Such a software will send GARP (Gratuituous Address Resolution Protocol) packet after failover.

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