Hosted application, DNS server setup?

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http://serverfault.com – Currently I'm allowing users to have an hosted application. Currently they have to point A-records to our servers (sometimes this is to hard or get's messy). I've seen other players using 2 dns servers, so that the user only needs to change these. I'm willing to implement this, but a lot of questions come up. What should I use for this? Can I use bind? The records need to be generated from a mysql database What type of servers do I need? Is a DNS server taking a lot of load? Currently having around 80K daily visitors. Thanks! (HowTos)