On 2015-10-02 1:23, Trevor Vaughan wrote:
I was talking with a few folks today about potential resolutions to
module namespace issues.
== Fundamental Issue ==
puppetlabs_apache -- Installs To --> apache
example42_apache -- Installs To --> apache
theforeman_apache -- Installs To --> apache
You get my point...
== Current Solutions ==
Right now, there are two ways to solve this problem if you want some of
your nodes to use puppetlabs_apache and others to use theforeman_apache.
1) Modify the module and force the namespace:
- puppetlabs_apache -- Installs To --> puppetlabs_apache
- theforeman_apache -- Installs To --> theforeman_apache
* Isssue: You can't just use outside code at will. You have to modify
*everything* that uses the above code.
2) You have to create a separate environment for each host group
(potentially each host) that you want to have use the differing code.
* Issue: This is a LOT of overhead for a couple of modules and may
have other ramifications in terms of performance as you get up in number.
So, would it be possible to allow multiple versions of a module to exist
in the same namespace but only use one during a given run?
Basically no, this is not possible without adding some kind of mechanism
to filter out modules on the modulepath. This will need to be done per
environment anyway. Remember that modules can contribute all sorts of
extensions to puppet (faces, indirections, facts, functions, types, and
with future parser also bindings). For performance reasons (and
bootstrapping, etc.) these are scanned when the environment loads (some
scans are lazy, but may take place before manifests really starts to be
evaluated).
- henrik
== The First Proposal ==
Inspired by RVM Gemsets, how about allowing modules to declare which
version of a given module they will use?
/etc/puppet/modules/apache/puppetlabs/{files,modules,manifests}
/etc/puppet/modules/apache/theforeman/{files,modules,manifests}
/etc/puppet/modules/apache/<author>/{files,modules,manifests}
Then, use could be dictated by something like: include apache@puppetlabs.
Unfortunately, this really comes down to the parser being able to
understand the following:
include apache => See if there are any @'s and use that one
include apache@puppetlabs => include the Puppetlabs apache
include apache@puppetlabs && include apache@theforeman => Fail, conflict
== Alternative ==
One possible alternative is to just use the metadata.json file to
dictate which module will be used when loading other modules.
Again, if there is a conflict, that is a failure but *only* if the code
attempts to use both at the same time.
The benefit here is that it should make things very unambiguous while
the drawback (if it really is) is that you *must* put a metadata.json
file in every module that you create.
This is just a set of thoughts that I hope get us moving in a direction
where this type of thing is possible and I look forward to hearing what
people think (good, bad, or ugly)!
Thanks,
Trevor
--
Trevor Vaughan
Vice President, Onyx Point, Inc
(410) 541-6699
tvaug...@onyxpoint.com <mailto:tvaug...@onyxpoint.com>
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