[rudder-dev] Best Practises for writing techniques

[Michael Gliwinski]

Thanks for your answer, before I start thinking about the rest, just a 
question about variables.  Just whenever you have time, just trying to 
understand what's going on :)

On Thursday 28 Feb 2013 18:31:24 Nicolas Charles wrote:
> > 3c. initial tests show it should be OK, but do you think there could be
> > problems using those variables from other (e.g. associated) techniques?
> 
> Unfortunately, yes, there could.
> We have no way do define the order in which the bundles will be 
> executed, so there is no guarantee that the variable will already be 
> defined when calling it from another technique (unless you define some 
> variables in the bundle common)

Would that be something different between how Rudder drives CFEngine and plain 
CFEngine?

I wrote a couple of tests yesterday and based my assumptions on that.  This 
appears to work, i.e. when running `cf-agent -f ./cf-test-var-deps.cf -KI` I 
get:

R: [master/master_config] mnt.technique_name = 'mnt'
R: [master/master_config] mnt_config.point[1] = '/tmp/mntbar'
R: [master/master_config] mnt_config.point[0] = '/tmp/mntfoo'
R: [master/master] master_config.foo = 'master'
R: [mnt/mnt_config] master_config.foo_file = '/tmp/foo'
R: [mnt/mnt_config] master_config.bar_file = '/tmp/bar'

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-------------- next part --------------
bundle agent master_config (technique_name)
{
  vars:
    any::
      "foo" string => "${technique_name}";
      "foo_file" string => "/tmp/foo";
      "bar_file" string => "/tmp/bar";
      "point_idx" slist => getindices("mnt_config.point");

  reports:
    a|!a::
      "[${technique_name}/master_config] mnt.technique_name = '${mnt.technique_name}'";
      "[${technique_name}/master_config] mnt_config.point[${point_idx}] = '${mnt_config.point[$(point_idx)]}'";
}
-------------- next part --------------
bundle agent master {
  vars:
    any::
      "technique_name" string => "master";

  methods:
    any::
      "master_config($technique_name)" usebundle => master_config("${technique_name}");

  reports:
    a|!a::
      "[${technique_name}/master] master_config.foo = '${master_config.foo}'";
}
-------------- next part --------------
bundle agent mnt
{
  vars:
    any::
      "technique_name" string => "mnt";

  methods:
    any::
      "mnt_config(${technique_name})" usebundle => mnt_config("${technique_name}");
}
-------------- next part --------------
bundle agent mnt_config (technique_name) {
  vars:
    any::
      "point[0]" string => "/tmp/mntfoo";
      "point[1]" string => "/tmp/mntbar";

  reports:
    a|!a::
      "[${technique_name}/mnt_config] master_config.foo_file = '${master_config.foo_file}'";
      "[${technique_name}/mnt_config] master_config.bar_file = '${master_config.bar_file}'";
}
-------------- next part --------------
# test if you can reference variables in parametrised bundles and
# if two bundles can reference each other's variables (like a circular dep)
# ans: both yes (whether defined in the same file or not)

body common control {
  inputs => { "cf-test-var-deps-master.cf", "cf-test-var-deps-master-config.cf", "cf-test-var-deps-mnt.cf", "cf-test-var-deps-mnt-config.cf" };
  bundlesequence => { "master", "mnt" };
}