On 2016-03-18 01:46, Ron wrote:
On Fri, Mar 18, 2016 at 12:12 AM, G.W. Haywood <b...@jubileegroup.co.uk <mailto:b...@jubileegroup.co.uk>> wrote:Hi there, On Thu, 17 Mar 2016, Ron wrote: ... in this case it's a supplier who is unable to keeps his DNS servers working, and we just want to keep the connectivity. I'd just put something in /etc/hosts and send myself an email every month or so to remind me I'd done that.This is what we're currently using, but it has the downside of not picking up ip address changes.
If you want to reinvent caching, why not go a step further, periodically query the records and build a local /etc/hosts
I've done this in a couple places where I need certain records to work even if DNS is broken. For example, it's just not worth having a NFS or Gluster filesystem mount fail because DNS happens to be down. If DNS is down, I'm probably already mid-panic, I don't need to worry about whether or remote file systems will come back up if I need to reboot a thing.
My current logic is that I do a SOA query and check the serial number, if it has changed, I query every needed hostname into a temp file, and if every single query was successful, check the SOA again, and if it still matches, update the /etc/hosts. If anything goes wrong (including a mismatch between the SOA), dump the temp file and try again.
Slaving the zones would be better, but some machines have a resolver already, sometimes with unique configuration that I couldn't bulldoze (and I'm too lazy to manually review the configuration of every machine) and sometimes the local resolver was Unbound, and also the master DNS server doesn't have a list of every machine that needs a NOTIFY, or a way to keep that list up to date. It was just faster to code up a sloppy /etc/hosts script to update a handful of critical records. Lame reasons, but it works well enough and hasn't blown up in my face yet.
-- Dave Warren http://www.hireahit.com/ http://ca.linkedin.com/in/davejwarren
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