On Tuesday, April 2, 2013 2:09:41 PM UTC-5, beyonddc...@gmail.com wrote:
>
> Hi All,
>
> I am new to Puppet and have a question on dependency cycle.
>
> I am currently applying my resource directly using the command prompt on
> Windows 'puppet apply --noop init.pp'.
>
> When I try to test it, I encounter a dependency cycle error.
> Error: Could not apply complete catalog: Found 1 dependency cycle:
> (Registry_key[delete_hklm_test_foo1_key_step_1_2] =>
> Registry_key[delete_hklm_test_key_step_1_3] =>
> Registry_key[delete_hklm_test_foo2_key_step_1_1] =>
> Registry_key[delete_hklm_test_foo1_key_step_1_2])
> Try the '--graph' option and opening the resulting '.dot' file in
> OmniGraffle or GraphViz
>
> My init.pp is like this.
>
> include deletion_key_only
> class deletion_key_only {
> registry_key { 'delete_hklm_test_foo2_key_step_1_1':
> ensure => absent,
> purge_values => false,
> path => 'hklm\software\Test\foo2',
> }
> registry_key { 'delete_hklm_test_foo1_key_step_1_2':
> ensure => absent,
> purge_values => false,
> path => 'hklm\software\Test\foo1',
> require => Registry_Key['delete_hklm_test_foo2_key_step_1_1'],
> }
> registry_key { 'delete_hklm_test_key_step_1_3':
> ensure => absent,
> purge_values => false,
> path => 'hklm\software\Test',
> require => Registry_Key['delete_hklm_test_foo1_key_step_1_2'],
> }
> }
>
> I am not sure why I hit a dependency cycle error because I thought I have
> the dependency lay out correctly on my manifest where
> 'delete_hklm_test_foo2_key_step_1_1' will go first, then
> 'delete_hklm_test_foo1_key_step_1_2' and family
> 'delete_hklm_test_key_step_1_3'.
>
> Can anyone please explain why I am encountering a dependency cycle error?
>
>
The dependency cycle is not caused directly by your code. I don't know
what 'registry_key' type you are using (since there isn't one in the Puppet
core), but it looks like it probably implements an autorequire based on the
registry path. The type documentation should mention that, but the meaning
of "autorequire" may not be evident.
The way it works for Files is that if both a file and its parent directory
are managed resources, AND no relationship between them is otherwise
declared, then Puppet automatically gives the file a "require" relationship
on its parent directory (hence "autorequire"). That is what you want in
most cases, because it is much more common to want to ensure a file (or
registry key) present, which requires the parent directory also to be
present, than to ensure it absent. When you want the file and parent
directory absent, however, it is the wrong order, and in that case you must
explicitly declare the correct ordering relationship. Puppet has
general-purpose support for autorequires, so it is likely that your
Registry_key type behaves similarly.
For your particular code, I would add:
before => Registry_key['delete_hklm_test_key_step_1_3']
to both the other Registry_key resources, and remove the then-redundant
'require' from Registry_key['delete_hklm_test_key_step_1_3']. That should
be more than enough to solve the problem, but I would also remove the
needless 'require' from Registry_Key['delete_hklm_test_foo2_key_step_1_2']:
it doesn't matter whether 1_1 or 1_2 is applied first, only that both are
applied before 1_3.
As a general rule, you should not attempt to model sequences of action in
Puppet. Instead, model only the true constraints on the order of resource
application, and let Puppet choose whatever order it likes that is
consistent with those constraints.
Whether you should use 'require' or 'before' relationships, or their
signaling counterparts, is a context-sensitive issue. I like 'before' in
this case because it allows the relationship to be owned by the child key,
which necessarily knows about its parent; the parent key, on the other
hand, should not be required to know about all its children.
John
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