Forum: CFEngine Help
Subject: Do a single DNS lookup
Author: sauer
Link to topic: https://cfengine.com/forum/read.php?3,23813,23813#msg-23813
So, our cfengine server layout basically has a single master, and then
secondary servers which are geographically distributed. The secondaries pull
the master policy from the central system, and then systems in each specific
geographic location pull the config from their local secondary. In order to
facilitate this, I have a single DNS entry which, when looked up, returns the
IP of the local server first, and then the others later. This makes my
configuration way simpler, as I just say "copy config from thesource.mydomain",
and DNS takes care of the rest.
Except that it doesn't work that way. It seems that each new promise which
references thesource iterates through the values returned in DNS. I'm pretty
sure this is a side effect of how the OS's resolver works, but I'm not positive
that it's not Cfengine instead. I therefore have two questions:
In the long term, i think it'd be handy to be able to configure how round-robin
DNS entries are handled. I'd like to see a common control parameter which
selects between "first", "random" and "round-robin" to control which IP
cfengine uses if the resolver provides multiple IPs for a name. I'll submit a
feature request shortly, but first I wonder if it's Cfengine rotating through
the results, or if it's the OS (this seems to happen on more than just Linux).
In the short term, I'd like a suggestion as to how I can just get an IP into a
variable once and use that for the rest of the evaluation. Avoid the
temptation to suggest something simple like this:
vars:
"master_ip" string => host2ip( "thesource" );
"master_host" string => ip2host( "$(master_ip)" );
Because that tosses out a bunch of warnings about variables being redefined
(due to the host2ip function returning different values on later runs). But
what about defining a class?
vars:
!g_havehost::
"master_ip" string => host2ip( "thesource" );
"master_host" string => ip2host( "$(master_ip)" );
classes:
"g_havehost" expression => regcmp(".+", "cfmaster_host");
Close, but no cigar. I get all sorts of weird behavior depending on the
bundlesequence used. Technically, the first one does work, but I really don't
like having warnings spit out - not only because they're indicative of a
less-than-elegant solution, but also because they obscure more important
warnings by training people to just ignore warnings.
_______________________________________________
Help-cfengine mailing list
Help-cfengine@cfengine.org
https://cfengine.org/mailman/listinfo/help-cfengine
