Forum: CFEngine Help
Subject: Re: Dealing with vars changing
Author: sauer
Link to topic: https://cfengine.com/forum/read.php?3,24603,24614#msg-24614
Because the order in which things appear in the file are more of a suggestion
than a requirement (declarative language and all) describing the order in which
promises are evaluated, I prefer to handle this with a pair of bundles. Bundle
the first is a common bundle which defines the classes which define a system
getting a non-default value (based on whatever other criteria), and a
meta-class which determines if a system gets the default or not (by combining
all of the override classes). The second bundle actually sets the vars based
on the common classes. So, here's an example. It could be made a little more
portable by making the common class name a variable passed in to the common
bundle as a parameter, making the override suffixes and criteria an array of
slists (also passed in as a parameter), and using ifvarclass in the vars
section of the agent bundle rather than regular classes. But I think the way I
posted it is way simpler to read. :)
Either way, though, I like this a lot better than using a free policy, because
there's no warnings about overriding variables or any such craziness - and the
variables are consistent across all three passes through the agent bundle;
there's no need to wait for the free variables to calm down on a second or
third pass. You separate out the critera for overriding from the actual
selection of a default or non-default value, resulting in easier-to-read
variable assignments through abstraction.
sauer@midnight:~$ cat ./conditionalvars.cf
#!/usr/local/sbin/cf-agent -Kf
body common control { bundlesequence => { "a" }; }
bundle agent a{
methods:
"prep" usebundle => prep_for_vars;
"go" usebundle => dostuff;
}
bundle common prep_for_vars {
classes:
"var_override_myval_1" or => { "host1", "host2" };
"var_override_myval_2" or => { "host3", "host4" };
"var_override_myval" expression => classmatch("var_override_myval_.*");
}
bundle agent dostuff {
vars:
any::
"default_myval" string => "default";
var_override_myval_1::
"myval" string => "Overridden to 1";
var_override_myval_2::
"myval" string => "Overridden to 2";
!var_override_myval::
#"myval" string => "$(default_$(this.promiser))";
"myval" string => "$(default_myval)";
reports:
cfengine:: "MyVal is '$(myval)'";
}
sauer@midnight:~$ ./conditionalvars.cf
R: MyVal is 'default'
sauer@midnight:~$ ./conditionalvars.cf -Dhost1
R: MyVal is 'Overridden to 1'
sauer@midnight:~$ ./conditionalvars.cf -Dhost3
R: MyVal is 'Overridden to 2'
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