Issue #2285 has been reported by James Turnbull.
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Refactor #2285: Improved Resource Identification
http://projects.reductivelabs.com/issues/2285
Author: James Turnbull
Status: Needs design decision
Priority: Normal
Assigned to: Luke Kanies
Category:
Target version: unplanned
Affected version: 0.24.8
Puppet currently uses what is known as the namevar to uniquely identify
resources, so you don't try to manage twice the same resource in the same
manifest. For example, in the case of files, the whole path of the file acts as
the namevar, so if you include two file resources with the same path in a
manifest puppet will abort showing an error.
This is not enough, as in certain cases the namevar parameter doesn't uniquely
identify a resource. For example, in Gentoo you may have two different packages
with the same name under different categories (dev-java/ant and app-vim/ant or
app-admin/sudo and app-vim/sudo, to name a few), so you wouldn't be able to
install both those packages with puppet, as it would think they are the same
one.
Proposed solution
Some changes have to be made in order to use puppet to handle such resources.
Here they are:
Compound keys
A compound key is a key that consist of two or more attributes. In the case of
puppet, types should be able to define which set of parameters form their key
to uniquely identify a resource, so you may have resources identified with a
set of parameters instead of a single parameter. For example, in the case of
packages, you may have that {category, name} uniquely identifies a package.
Per provider specific parameters
Although at first it may seem this is not directly related to the problem of
improved resource identification, it's an important part of the solution.
Puppet tries to abstract away from the implementation details, and in the
abstraction process there are some bits of information that are lost: you
cannot intend to create a type with parameters for all the possible
implementation details for that type out there. So sometimes you find that you
can't access some key functionality in your system because the puppet type
doesn't take into account all those implementation details. For example, there
are lots of parameters in package managers you can't access using puppet, as it
would be unmanageable to have a type with every imaginable parameter from every
imaginable package manager.
Anyway, as there is the need to access some of that functionality, some puppet
types currently have some parameters that are applicable only to some provider.
As we can't expect to have every parameter for every type provider in the type,
we should follow another path: per provider specific parameters.
In this case, a provider should be able to define its own set of parameters, so
we would be able to access functionality for that specific provider without the
need to add parameters to the generic type, that would still handle the basic
aspects of the resource.
Addition of per provider specific parameters to compound keys
The concept of unique resources may change from platform to platform (from
provider to provider in puppet's terminology). For example, Gentoo has what is
known as slotted packages: you may have Apache 1 and 2 installed in the same
system, with different sets of configuration files, just in case you need to
run both version of the package. While in other platforms the package Apache
would be uniquely identified by its name, in Gentoo you would need an
additional attribute to identify it (slot in this case), so a package resource
in Gentoo is uniquely identified by the tuple {category, name, slot}.
It's clear that slot is specific to the Gentoo platform and the portage
provider, so providers should be able to add some of its parameters to the key
of the corresponding type, so they can tweak the concept of oneness.
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