[Puppet Users] Re: 'require' option is ignored?

[jcbollinger]

On Thursday, February 15, 2018 at 9:46:17 AM UTC-6, buoyant_puppy wrote:
>
> Got it, thanks everyone.
>
> Just one small point to add - I'm not actually directly concerned with 
> Execs here. If you look at my original example, I was needing to do a 
> conditional check like "if directory exists then...", and my Exec-based 
> solution for it is just an ugly workaround. I understand the puppet 
> philosophy here is focused on being declarative, but it's just extremely 
> common that we don't have the pleasure of working in a purely declarative 
> environment. As such I think it'd be nice to see unless/requires/etc evolve 
> further.
>


You are not the first to express an interest in Puppet developing in that 
direction, but Puppet already has mechanisms for the kind of thing you 
describe.  The main approaches to adapting to target-machine state are

   1. to rely on *facts* collected from the node to influence details of 
   the catalog.  To this end, there are well-developed facilities for defining 
   and distributing your own custom facts.
   2. to rely on resource providers to behave appropriately for the target 
   environment; this is under the control of provider developers, including 
   you if you wish to be one.

These are well-matched to Puppet's model of operation, which is to first 
compute a target state based on the machine's identity and current state, 
site manifests, and site data (catalog building); then to attempt to take 
whatever action is needed to put the machine in that state (catalog 
application).  A key aspect here is that the target state embodied by a 
catalog is unconditional at the level of abstraction of the catalog, and 
perhaps that's what you mean by "purely declarative".  But although that 
perhaps fits the catalog, it does not fit Puppet DSL at all, nor, 
therefore, the overall system.

In the past, I have been fond of saying "Puppet is not a script engine."  I 
consider that a strength, not a weakness.


John

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[Puppet Users] Re: 'require' option is ignored?

[buoyant_puppy]

Got it, thanks everyone.

Just one small point to add - I'm not actually directly concerned with 
Execs here. If you look at my original example, I was needing to do a 
conditional check like "if directory exists then...", and my Exec-based 
solution for it is just an ugly workaround. I understand the puppet 
philosophy here is focused on being declarative, but it's just extremely 
common that we don't have the pleasure of working in a purely declarative 
environment. As such I think it'd be nice to see unless/requires/etc evolve 
further.


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[Puppet Users] Re: 'require' option is ignored?

[jcbollinger]

On Thursday, February 15, 2018 at 8:17:20 AM UTC-6, jcbollinger wrote:

> This has been a point of confusion with the Exec resource type for the 
> whole nine-ish years that I have been involved with Puppet.  Maybe it's 
> time to actually file an issue against the docs to get it cleaned up.
>
>
And here's an issue for that: 
https://tickets.puppetlabs.com/browse/DOCUMENT-818.


John

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[Puppet Users] Re: 'require' option is ignored?

[jcbollinger]

On Thursday, February 15, 2018 at 4:41:59 AM UTC-6, buoyant_puppy wrote:
>
> I think I got this. My main issue was the 'true' logic with an 'onlyif', 
> because that's always only going to either run (= and therefore meet the 
> requirement) or not run at all (= which also meets the requirement since 
> it's not a failure).
>
>

Yes, I think that covers it.

 

> I feel the choice of words here leaves room for confusion. Like 
> "unless"... unless succeeds? unless fails? "requires" also leaves some 
> amgiuity as well, since it considers the requirement met as long as the 
> required resource did not explicitly return a failure. So "notrun" is just 
> as good as success, which to me doesn't really intuitively match what I 
> think "require" means.
>
>

This has been a point of confusion with the Exec resource type for the 
whole nine-ish years that I have been involved with Puppet.  Maybe it's 
time to actually file an issue against the docs to get it cleaned up.

But I don't think it's an issue with the metaparameter names.  Rather, it's 
a problem with the overall characterization of an Exec resource, which is 
not well addressed by the current docs.  I most recently answered 
essentially this same question over at StackOverflow 
.
  
Here's the heart of it:

Like any other resource, Execs model target-machine state, though in their 
case, that state is local to the context of one catalog run. Often it is 
described as whether the Exec's command has been run or not, but it is 
better characterized the other way around, as whether the Exec's command *needs 
to be run* or not. If it is in the "needs to be run" state then 
successfully executing the Exec's command transitions it to the "does not 
need to be run" state.


The unless, onlyif, and creates properties of an Exec serve to determine 
the initial state of the corresponding physical (so to speak) resource. If 
none of them are provided then the physical resource is initially in the 
"needs to be run" state. If one or more of them is provided then they may 
indicate that the Exec initially is in the "does not need to be run" state. 
*And 
that's the target state*. In that case, then, the Exec is successfully 
applied without running its command.


I've given substantially the same answer before in this group, too.


John

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Re: [Puppet Users] Re: 'require' option is ignored?

[R.I.Pienaar]

On Thu, 15 Feb 2018, at 11:41, buoyant_puppy wrote:
> I think I got this. My main issue was the 'true' logic with an 'onlyif', 
> because that's always only going to either run (= and therefore meet the 
> requirement) or not run at all (= which also meets the requirement since 
> it's not a failure).
> 
> I feel the choice of words here leaves room for confusion. Like "unless"... 
> unless succeeds? unless fails? "requires" also leaves some amgiuity as 

"unless this thing is true" seems clear to me, also in line with how ruby works 
and also puppet

  if $thing { }
  unless $thing { }


> well, since it considers the requirement met as long as the required 
> resource did not explicitly return a failure. So "notrun" is just as good 
> as success, which to me doesn't really intuitively match what I think 
> "require" means.

require means the required resource is in the desired start.  Your desired 
state is not to run at certain times, the desired behavior was reached so the 
resource is in pass state.  require is a generic meta param that applies to all 
resources - it does not know the particulars of what you think a certain 
resource is doing, its at a higher level.

> 
> Here's a set of tests that illustrate all this more clearly, in case it 
> helps someone else that stumbles on this post:
>   exec { "test1": command => "/bin/false", unless => "/bin/true" }  # 
> unless = only if this fails
>   notify { "false, unless true fails, which it wont: this should not fail 
> (notrun) and i should see this": require => Exec["test1"] }
>   exec { "test2": command => "/bin/false", onlyif => "/bin/true" }   # 
> onlyif = only if this returns true
>   notify { "false, but only if true: this should fail and i should not see 
> this": require => Exec["test2"] }
>   exec { "test3": command => "/bin/true", unless => "/bin/true" } # unless 
> = only if this fails
>   notify { "true, unless true fails, which it wont: this should not run 
> true (notrun) and i should see this": require => Exec["test3"] }
>   exec { "test4": command => "/bin/true", onlyif => "/bin/false" } # onlyif 
> = only if this returns true
>   notify { "true, but only if false returns true, which it wont: true will 
> be run and i should see this": require => Exec["test4"] }
> 
> 
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[Puppet Users] Re: 'require' option is ignored?

[buoyant_puppy]

I think I got this. My main issue was the 'true' logic with an 'onlyif', 
because that's always only going to either run (= and therefore meet the 
requirement) or not run at all (= which also meets the requirement since 
it's not a failure).

I feel the choice of words here leaves room for confusion. Like "unless"... 
unless succeeds? unless fails? "requires" also leaves some amgiuity as 
well, since it considers the requirement met as long as the required 
resource did not explicitly return a failure. So "notrun" is just as good 
as success, which to me doesn't really intuitively match what I think 
"require" means.

Here's a set of tests that illustrate all this more clearly, in case it 
helps someone else that stumbles on this post:
  exec { "test1": command => "/bin/false", unless => "/bin/true" }  # 
unless = only if this fails
  notify { "false, unless true fails, which it wont: this should not fail 
(notrun) and i should see this": require => Exec["test1"] }
  exec { "test2": command => "/bin/false", onlyif => "/bin/true" }   # 
onlyif = only if this returns true
  notify { "false, but only if true: this should fail and i should not see 
this": require => Exec["test2"] }
  exec { "test3": command => "/bin/true", unless => "/bin/true" } # unless 
= only if this fails
  notify { "true, unless true fails, which it wont: this should not run 
true (notrun) and i should see this": require => Exec["test3"] }
  exec { "test4": command => "/bin/true", onlyif => "/bin/false" } # onlyif 
= only if this returns true
  notify { "true, but only if false returns true, which it wont: true will 
be run and i should see this": require => Exec["test4"] }


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