Recently, I have such a bad luck finding a reliable hosting company (despite all the good advice at WebmasterWorld). They all self-rate themselves with 99.99999999... uptime, which is just a bunch of lies. Please tell me what would happen if I do this: 1. get two hosting accounts with two different companies - each gives me two name servers 2. I update the nameservers at my registrar by using all 4 nameservers 3. both accounts are mirror images of each other at all times What happens when one server fails? Do I have increased reliability, or do wierd things start happening which, due to my ignorance on the subject, I am not able to forsee? A side note - I would to this just on a single site for which it is absolutely necessary to be up ALL the time, so I wouldn't mind extra hassle and expense
This will work in general, however, since there will be two physical websites, you may run into a problem maintaining state for your visitors. That is, if you add multiple www hosts to all DNS four servers (i.e. each DNS server will have two or more www records pointing to both of your websites), then some HTTP requests from the same user may potentially end up on a different web server and user's state passed through session cookies will be lost. There are ways to resolve this, but they all require some control over your machines (e.g. you can set up IIS with a standalone state server, which two or more IIS servers share to maintain cookies). If you are just after a more reliable DNS service, just get yourself a backup DNS service. Google dns backup. J.D.
Thank you very much DNS backup is exactly what I need. I didn't even know that such service existed. I am just curious - the problem of losing user's state that you are refering to - wouldn't that happen only when both nameservers of the primary host fail? Or would domain resolve to 3rd and 4th nameserver (2nd host) more often (presumably for some other reason than failure of the two primary ones)?
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This doesn't relate to DNS, though. Presumably, you are getting multiple DNS servers to run more than one web server (same domain, same website, different machines). By default, web servers store each visitor's session information (state) in memory; since you will have more than one web server (i.e. physical machines), you may end up having two independent states for the same user - one on each server. In other words, when a user wants to visit your website, their browser does a DNS lookup and gets two IP addresses - one for the web server A and another for B. The browser picks one, say A, and the user logs in; your website sends them a cookie that identifies this user's session. Because there's more than one IP address returned, one of the subsequent requests may be submitted to the second IP address, web server B, which knows nothing about this cookie or user. As a result of this, the user who was logged on, will all of a sudden see an access-denied message of some kind. J.D.