On 2013-05-22 16:00, jcbollinger wrote:
On Wednesday, May 22, 2013 1:48:26 AM UTC-5, David Schmitt wrote:
Just because it is not well known. ensure_packages seems to be designed
for exactly the use-case you are describing: you have two modules both
requiring the same utility packages without caring at all about
versions or
anything else.
To elaborate: contrary to (most, all?) other resources, packages
have this
no-parameter use case, which allows conflict-free merging. Managing
more
complex resources (users, files) would require more cooperation between
modules to ensure that the different requirements do not step on each
other.
No, the only resource types that could have no-parameter use cases would
be those with no parameters, but there are none such. Some types,
including Package, admit sensible use cases involving only default
parameter values, but that's a rather different thing, and not
necessarily the thing you want. Also, either ensure_packages() must
ignore the context-specific Package parameter defaults (in which case
those won't work, which could be a hard-to-debug surprise) or else uses
of the function in different contexts can be inequivalent, so that one
set of package parameters is chosen over all others, at semi-random
(also a potential nasty surprise).
Furthermore, ensure_packages() is inherently parse-order dependent, and
parse-order dependencies are a major source of concern in Puppet
manifest design. That is mitigated in this case if you require that
packages used with ensure_packages() are never declared any other way,
but then you're placing a constraint on your manifest set that is easy
to overlook, that might not be enforced by the catalog compiler, and
that you cannot by any means expect third-party modules to comply with.
Ensure_packages() is bad juju. If you design your manifest set well in
the first place then you will not need it. Sadly, the current state of
module compatibility is that in some cases you may need to refactor
third-party modules to achieve the overall design criteria you want. At
least Puppet will notify you of those cases (provided that
ensure_packages() or some similar device doesn't mask it).
I totally agree with your sentiment in theory, but would like to note
that in practice, "ensure_package('wget')" is an efficient and low-risk
way to solve a real problem across otherwise non-cooperating modules.
Please also note, that in my years of module writing, I only encountered
a handful of packages that should be given this treatment. Wget and
rsync being the most prominent of those.
Regards, David
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