anchor pattern and class containment status

[Tim Mooney]

All-

We're currently using puppet 2.7.14 on master and all clients.

I thought I understood why 'anchor' is part of stdlib, but after
re-reading both

http://projects.puppetlabs.com/projects/puppet/wiki/Anchor_Pattern

and

http://projects.puppetlabs.com/issues/8040

yesterday in preparation for trying to explain it to one of our team
that's coming up to speed on puppet, now I'm not so certain I really
understand.

Specifically, is it necessary to use the anchor pattern if your module
only defines resources and doesn't require or include any other classes?

For example, if I have

class benthic {

group { 'squarepants':
ensure => present,
gid => '99999',
}

user { 'spongebob':
ensure => present,
uid => '99999',
gid => 'squarepants',
home => '/home/pineapple',
}

package { 'starfish':
ensure => present,
}

file { '/etc/starfish.conf':
ensure => file,
owner => 'root',
group => 'squarepants',
mode => '0640',
source => 'puppet:///benthic/starfish.conf',
require => [
Package['starfish'],
User['spongebob'],
],
}

service { 'i_m_ready',
ensure => running,
enable => true,
require => Package['starfish'],
}
}

Given that class, do I need to use anchors to ensure that the
group/user/package/file/service resource graph is correctly attached to
(contained within) Class['benthic'], so that if some other module does

someresource { 'whatever':
...
require => Class['benthic'],
}

it just works, or, should I augment my class to also have

anchor { 'benthic::begin': }
anchor { 'benthic::end': }

Anchor['benthic::begin'] -> Group['squarepants']
Service['i_m_ready'] -> Anchor['benthic::end']

?

My resources within the class are using explicit "require" when necessary
and relying on puppet's automatic "require" logic in other places so
they are correctly ordered, but it's not clear from the pattern document
in the wiki or the ticket whether the issue is solely with nested
classes, or whether it's important to also use the pattern for standard
resources.

Also, the ticket was with respect to 2.6. I know this hasn't changed for
2.7, but is there anything in 3.0 that addresses the issue?

Tim
--
Tim Mooney Tim.M...@ndsu.edu
Enterprise Computing & Infrastructure 701-231-1076 (Voice)
Room 242-J6, IACC Building 701-231-8541 (Fax)
North Dakota State University, Fargo, ND 58105-5164

[Dan Bode]

On Wed, Oct 3, 2012 at 2:57 PM, Tim Mooney <Tim.M...@ndsu.edu> wrote:

All-

We're currently using puppet 2.7.14 on master and all clients.

I thought I understood why 'anchor' is part of stdlib, but after
re-reading both

        http://projects.puppetlabs.com/projects/puppet/wiki/Anchor_Pattern

and

        http://projects.puppetlabs.com/issues/8040

yesterday in preparation for trying to explain it to one of our team
that's coming up to speed on puppet, now I'm not so certain I really
understand.

yep, its probably the most confusing part of Puppet :(

 

Specifically, is it necessary to use the anchor pattern if your module
only defines resources and doesn't require or include any other classes?

you only have to use the anchor pattern when you need to depend on a class that has classes defined in it. The example below does not need the anchor pattern.

 

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[jcbollinger]

On Wednesday, October 3, 2012 4:59:58 PM UTC-5, Tim Mooney wrote:

All-

We're currently using puppet 2.7.14 on master and all clients.

I thought I understood why 'anchor' is part of stdlib, but after
re-reading both

         http://projects.puppetlabs.com/projects/puppet/wiki/Anchor_Pattern

and

         http://projects.puppetlabs.com/issues/8040

yesterday in preparation for trying to explain it to one of our team
that's coming up to speed on puppet, now I'm not so certain I really
understand.

Specifically, is it necessary to use the anchor pattern if your module
only defines resources and doesn't require or include any other classes?

No, not as I understand it.  The problem is that in Puppet 2.6 and maybe 2.7, classes are not directly represented in the relationship graph.  Therefore, if you declare a relationship where one end is a class, it appears in the graph as a collection of relationships with the resources declared by that class.  If both ends are classes then you get n x m relationships, where n and m are the numbers of resources declared by the two classes.

The need for the anchor pattern arises because the generated relationships to a class Foo's resources do not include relationships to resources declared by classes declared in the body of Foo, and because declaring a class (except via the 'require' function) does not create a relationship between the declaring and declared classes.

The anchor pattern involves using relationships to resources declared directly by Foo to bound the application order of classes declared by Foo.  Anchors are not needed for resources declared directly by Foo (else the anchor pattern wouldn't work in the first place).  The stdlib provides the special 'anchor' resource type specifically for this purpose, but resources of any other type could be used as well.

If Foo does not declare any other classes, then it gains no advantage from the anchor pattern.  If the needed ordering of interclass relationships is declared some other way, then the anchor pattern is unneeded.  If and when classes gain direct representation in the relationship graph (maybe it's happened already?), with (optional?) relationships to their included classes, the anchor pattern will no longer be needed.


John

[Ryan Coleman]

On Wed, Oct 3, 2012 at 2:57 PM, Tim Mooney <Tim.M...@ndsu.edu> wrote:

> I thought I understood why 'anchor' is part of stdlib, but after
> re-reading both

I suspect Dan & John have covered this well enough for you but I
wanted to point out a nice piece of the Puppet reference manual that
covers this. http://docs.puppetlabs.com/puppet/2.7/reference/lang_containment.html#known-issues

It explains things better than I ever could. If it's still not clear
enough, please consider filing a ticket against our docs for
improvement: https://projects.puppetlabs.com/projects/puppet-docs

[Tim Mooney]

In regard to: Re: [Puppet Users] anchor pattern and class containment...:

> On Wed, Oct 3, 2012 at 2:57 PM, Tim Mooney <Tim.M...@ndsu.edu> wrote:
>
>>
>> All-
>>
>> We're currently using puppet 2.7.14 on master and all clients.
>>
>> I thought I understood why 'anchor' is part of stdlib, but after
>> re-reading both
>>

>> http://projects.puppetlabs.**com/projects/puppet/wiki/**
>> Anchor_Pattern<http://projects.puppetlabs.com/projects/puppet/wiki/Anchor_Pattern>
>>
>> and
>>
>> http://projects.puppetlabs.**com/issues/8040<http://projects.puppetlabs.com/issues/8040>

>>
>> yesterday in preparation for trying to explain it to one of our team
>> that's coming up to speed on puppet, now I'm not so certain I really
>> understand.
>>
>
> yep, its probably the most confusing part of Puppet :(

:-) I think I would vote for create_resources() in that competition.

>> Specifically, is it necessary to use the anchor pattern if your module
>> only defines resources and doesn't require or include any other classes?
>>
>
> you only have to use the anchor pattern when you need to depend on a class
> that has classes defined in it. The example below does not need the anchor
> pattern.

Thanks Dan! The info from you & John & Ryan has been very helpful.

[Tim Mooney]

In regard to: Re: [Puppet Users] anchor pattern and class containment...:

> On Wed, Oct 3, 2012 at 2:57 PM, Tim Mooney <Tim.M...@ndsu.edu> wrote:
>> I thought I understood why 'anchor' is part of stdlib, but after
>> re-reading both
>
> I suspect Dan & John have covered this well enough for you but I
> wanted to point out a nice piece of the Puppet reference manual that
> covers this. http://docs.puppetlabs.com/puppet/2.7/reference/lang_containment.html#known-issues

Thanks Ryan, and thanks especially for the rewritten reference. I haven't
been through all of it yet, but the parts I've seen are excellent.

> It explains things better than I ever could. If it's still not clear
> enough, please consider filing a ticket against our docs for
> improvement: https://projects.puppetlabs.com/projects/puppet-docs

I created

https://projects.puppetlabs.com/issues/16783

which mentions what I think might be a bug in the second example on that
page and also asks for a little clarification.

Thanks again for the pointer to the docs!