On Monday, September 16, 2013 7:40:35 AM UTC-5, Adeel Bhatti wrote:
>
> Thanks for your reply !
> This would be really cool if the agent can look and identify the manifect
> changes !
> I have a service restart in my class, so I want to execute that only if
> there is some change in the configuration/manifest !
> Regards
> Adeel
>
>
Puppet can do that. See below.
In answer to your original question, it is usual for each Puppet client to
run the agent on a regular schedule, either using its built-in daemon mode
(i.e. running it as a service) or via an external scheduler, such as cron.
That way there is no need to touch individual clients to roll out
configuration changes -- it is sufficient to change the manifests and/or
data on the master.
It is important to understand that Puppet is a state management service,
not a script engine. The distinction shows up here in that the Puppet
agent's normal behavior is to check the properties of each managed
resource, and to apply only those changes needed to put it into the target
state. Resources that are already in the target state are not changed in
any way.
Thus, whenever the agent modifies a resource, such as a service's
configuration file, it constitutes a genuine change. Puppet has a
mechanism for notifying resources about such changes in other resources,
and it is particularly well supported for exactly the situation you
describe: restarting services when their configuration changes. It can
look like this:
file { '/etc/myservice.conf':
ensure => 'file',
content => template('myservice.conf.tmpl'),
# ...
}
service { 'myservice':
enable => true,
ensure => running,
subscribe => File['/etc/myservice.conf']
}
The magic is in the 'subscribe' parameter. It says that the service needs
to be "refreshed" if the agent applies any changes to the referenced file
resource. The meaning of "refresh" varies by resource type, but for
services it means to restart the service.
John
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