Fault tolerant web servers and DNS - on the cheap
The simplest ideas are the best, and despite a small amount of ridicule, I think I have seen possibly the most efficient failover solution yet. It is quite simple, there are two web servers, say A and B and one DNS server. According to the DNS server A is www.wlv.ac.uk – Server B is an exact clone – but is not used. A script is then used to ping (or similar) A, when it does not reply, the script considers A to be down, and therefore switches its DNS entry to B’s IP address, an email is sent and an action is taken to fix the server A, whilst the script continues to monitor B.
This is obviously not the most ideal solution for a serious company thinking about failover – as there are many single points of failure, but hey – if it works it works.
posted by Richard Francis @ 10:40 am
4 Comments:
How about having more than one dns - a nice linux box that tests the 'live' dns and takes over should it fail. Perhaps implement a shutdown (of the broken server) then a reconfig of the replacement.
Thats not a bad idea - after all in this sort of situation you'd be looking for 100% uptime, and therefore you will want to remove any single points of failure. This of course will add to the cost, therefore, say if you have all the fault tollerance in the world and your link goes down you have not improved uptime and therefore depending on paranoia you will have to look for a secodary link provider - adding to the cost.
Cheers Matt ;)
The trouble is both of those DNS servers are usually on the same network, so if you have a network failure both dns are lost. In my plan you could have more than one line each with its own dns. Not sure how this would work in practise lot of expense and complications.
I suppose on a cheap version of DNS you could nick dyn-dns' theory and even just use their DNS servers - i'm sure they'll have failover - not sure exactly how that would work tho - although my router automatically re-registers with dyn-dns. . .
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