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I'm trying to get my head around how this aspect of my server works and am uncertain I'm understanding it correctly. I'm looking for either confirmation my assumptions below are correct or correction to the assumptions.

The situation:

We have a dedicated server (running WHM & cPanel) which has multiple sites, including our own. We also have a couple of subdomains pointed to other servers and our email is hosted by a different service as well. Our NS records all point to our dedicated server. The setup is roughly as follows:

  • site.com : our dedi server
  • support.site.com : 3rd party service (zendesk)
  • status.site.com : our dedi server (temporarily)
  • emails / MX : 3rd party service (rackspace)

status.site.com is temporarily on our server, but I'm looking to move this to a separate server - I can't report downtime if status.site.com is down too!

We had some downtime recently due to a data center issue, and here's what happened when we did:

  • site.com : down (obviously)
  • support.site.com : accessible
  • status.site.com : down
  • emails : down

My assumptions then are as follows (please correct if I'm wrong!!):

  • support.site.com has a CNAME record that points to the 3rd party server. Was this why subdomain was still accessible while the main server was down?
  • email has the MX records set to point at the 3rd party service. Do the MX records work differently and have to buzz the server before bouncing on to the 3rd party service? Why is this different from how the subdomain worked?

Also, assuming I setup a separate server to host status.site.com, can I assume that this should then continue to function as support.site.com did in the event of server downtime?

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The major flaw in your setup is that you host your DNS on your server (and only on your server). This is always a bad idea. Optimally, you will host DNS on two servers in two different networks/datacenters and if you do this, everything that's not dependent on your main server will continue to work, include the support.example.com and the mail service (and the status site if it's on another machine). Using a 3rd party provider for DNS hosting is a perfect viable approach and I would recommend it over running your own.

support.example.com most likely was only still working because the CNAME resolution was still cached on your clients.

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  • so, I need to setup a 2nd DNS host and add it to the NS records, is that correct? – Aninemity Jul 15 '15 at 13:44
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Whats the TTL for support.site.com ? Depending on time value set ,this could explain why sub-domain was still active. As the record had not been re-advertised. The cache on the record had not expired ,so there was need to query the DNS for the domain. The MX entries,how have you assigned them the priorities. This could explain why email was no longer available during the downtime. Its also advisable to split the name-severs to different geographical regions ,to avoid having a single point of failure.

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