[chef] Re: detect if a service is running?

[Daniel DeLeo < >]

On Friday, January 9, 2015 at 3:31 PM, James Harrison wrote:

> Hi chefs,
>  
> I’m pretty new to chef, and feel like I’m missing something obvious. Any 
> advice would be appreciated. I’m trying to cover two scenarios with one 
> recipe, in a Windows environment. What I’m trying to do is:
>  
> - Scenario 1: install a package  
> - Scenario 2: if the package is already installed, stop a service and then 
> reinstall the package.
>  
> The recipe, as currently written, goes through a series of steps involving 
> downloading the installer, always attempting to stop the service, then 
> running the installer if the package is not already installed, then 
> starting the service.  
>  
> The problem I’m facing is in scenario 1. If I attempt to stop the service, 
> but the service is not installed, then I receive an exception and execution 
> of the recipe halts.
>  
> Am I trying to do something that is better covered by two recipes? Or is 
> there some easy way to check if a service is installed?  
>  
> Thanks
>  
> James


A few things here. Firstly, our platform abstraction code is generally pretty 
tightly coupled to providers, which are also responsible for providing 
idempotent behavior, why-run support, logging events, and all sorts of things 
not related to, say, talking to the service manager or package manager. Which 
means that Chef doesn’t provide a nice abstract way of querying these things. 
So to meet your requirement to check if a package or service is installed, 
you’re best off running the command yourself.

As for how you accomplish that, there are a few ways. In the other branch of 
this thread, it was suggested to use `notifies`, but Chef doesn’t provide a 
“before notification,” which is what you’d need to stop the service before 
the package is upgraded (but only if it’s going to be upgraded). So one way 
or another, you’re going to have to write some code that can tell you if the 
package is about to be upgraded and will stop the service if that check 
returns true. You can use `shell_out` (specifics about doing this depend on 
whether you’re on Chef 11 or 12) to run a command and give you the return 
code and output. Once you have that, it might be as simple as adding a 
resource like:

service “stop FOO service before upgrading” do
  # other important stuff
  action :stop
  only_if { about_to_upgrade_package_foo? } # Ruby convention: true/false 
methods named w/ question mark
end

# resources to install/upgrade package, start service

HTH,

--  
Daniel DeLeo