On Fri, Dec 3, 2010 at 9:04 AM, Lars Francke <lars.fran...@gmail.com> wrote:
> Hi!
>
> Again thank you for the detailed answer.
>
>> One of the things that sometimes gives Puppet newbies trouble is that
>> it employs a declarative model rather than an imperative one. In
>> other words, it's an expert system, not a scripting language. The
>> Puppet language is all about describing the state that your system
>> should have, and Puppet later uses that description to ensure that
>> your system is in that state. This is very powerful and flexible, but
>> sometimes confusing, too. It is the core reason why you cannot
>> declare duplicate resources.
>
> I think I got all that.
> I have one problem though. Even spelling it all out won't work. Or to
> put it better: I don't know how.
> And add to that that we're changing our infrastructure quite
> frequently at the moment so I'd have to switch back and forth quite a
> lot of code if I got it to work.
>
> What I don't understand:
> I have an array $disks = ["/a", "/b"]
>
> And I can use that as the title of resources to define one resource
> for each member of the array. So far so good.
>
> file { $disks: }
> works as expected. And is expanded to:
> file { "/a": }
> file { "/b": }
> which are two distinct titles so work as expected. But those aren't
> the paths I need to manage.
>
> But what I want is:
> file { "${disks}/foo": }
>
> Being expanded to:
> file { "/a/foo": }
> file { "/b/foo": }
>
> What really happens:
> file { "/a/b/foo": }
A custom function that expands the array would be a bit more
universal, but you can still do this with puppet define resource type
with no ruby code:
define hadoop::mount {
file { "/mnt/${name}/hadoop":
ensure => directory,
owner => "root",
group => "hadoop",
require => Package["hadoop-0.20"]
;
}
}
hadoop::mount {
["disk1", "disk2", "disk3"]:
}
notice: /Stage[main]//Hadoop::Mount[disk2]/File[/mnt/disk2/hadoop]/ensure:
is absent, should be directory (noop)
notice: /Stage[main]//Hadoop::Mount[disk1]/File[/mnt/disk1/hadoop]/ensure:
is absent, should be directory (noop)
notice: /Stage[main]//Hadoop::Mount[disk3]/File[/mnt/disk3/hadoop]/ensure:
is absent, should be directory (noop)
mnt and hadoop can be a an variable for the defined resource so it's
supports generic file path: "/mnt/${name}/hadoop":
> It's obvious to me why this happens (the variable being in a string
> etc.) but I'd still love a way to allow me to do what I want because I
> think that would solve all my problems (I might be wrong here
> obviously).
>
> As I said earlier: I'm at a point where I don't know how to solve my
> problem even if I am as verbose as I can.
> I've just pushed my current (non-working) configuration to Github:
> https://github.com/lfrancke/gbif-puppet/blob/master/modules/hadoop/manifests/init.pp#L22-58
>
> I've spelled out all the main directories here in a virtual resource
> definition but I have no idea how to go on from there. Some machines
> need only two of those, some need all. The datanode[1] and namenode[2]
> classes need subdirectories "/dfs" everywhere and again this is with
> two different configurations (2 vs. 6 disks) and the tasktracker[3]
> and jobtracker[4] need a "/mapreduce" directory in there. Because
> those classes all need the common super directory, that's why I made
> it virtual. But how Do I realize it? I can't just list the
> realizations in the classes because they are different depending on
> the node.
The difference between the system can be written as a custom fact, a
variable set at top scope when defining the nodes, or use parametrized
class (available in 2.6).
class demo ($disk) {
case $disk {
"2" : { # add resource specific for 2 disk }
"6" : { # add resource specific for 6 disk }
}
# common for all system using class demo
}
node server1 {
class { "demo": disk => 2 }
}
node server2 {
class { "demo": disk => 6 }
}
Thanks,
Nan
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