Why can't I debug my puppet code? - eclipse

Question

I'm learning Puppet and the biggest frustration I have with the entire paradigm is the try/run/fix development process I'm using to build functional Puppet code. My background is in Java and I'm naturally use to debugging my code to find errors instead of just running the program to see where it bombs making development much faster but I can't seem to find a way to do this using Puppet and Eclipse. I know writing a debugger for Puppet would require some creativity given its nature but I think this is something the community could really benefit from.
I've written debuggers and know the Eclipse SDK but unfortunately it does not map cleanly to the Puppet architecture which is a bit awkward in the sense its runtime stack and execution flow does not happen in natural order as well as the fact the runtime requires a target machine to apply changes on.
I'm curious if the community has done any development work on trying to create some kind of debugger where code can be stepped. To write this I think it would make sense to extend Eclipse with a new Puppet debug configuration type where you specify a target sandbox host to test your code as well as a puppet project in your workspace you want to debug (leveraging existing Gepetto tooling). Then when you start a new Puppet debugging session Eclipse could connect to the remote host, execute puppet apply with some additional debug arguments and somehow provide feedback from the runtime about what line of code is currently being executed.
This still might be awkward but would allow puppet developers to quickly see things like oh duh.. I can't create this directory because the parent path does not exist, wait... why is this if statement not going here like I planned, oh I see here that Puppet is not very clear on single or double quotes or now I see why this fails because this class was not executed first etc. etc.
Instead all we get is a big ugly output on the agent console that yes can give us insight on errors but does not cleanly map exceptions to our code that in my view shows an underlying pain and weakness of Puppet, can you at least give me a stack trace and line number so I know where to look? Nope sorry.
Don't get me wrong, I love how Puppet can make me look very productive throughout the work week when all I'm doing is running Puppet apply on new machines which my manager has not yet figured out but I think for Puppet to really be useful this lack of debugging support is something that needs to be addressed.
Does anyone else feel this pain? - Duncan Krebs

Answer 1

It would be impossible to "step through" puppet code, unless you want to debug against the ruby codebase itself. It's not just that the order of "execution" is unclear, its that the manifest themselves are never executed at a single time. They are actually evaluated in multiple phases throughout execution.
There are ways to simplify finding problems though. The biggest one is writing unit tests using rspec-puppet. It lets you essentially test the compilation phase of puppet, helping you catch errors like circular dependencies, incorrect conditional logic, etc.

Answer 2

There is a new tool called the puppet-debugger which allows you to set breakpoints in your puppet code in order to step through it. So this is no longer "impossible" as it has been available for about 8 months.
You will first need to install the puppet-debugger gem
https://github.com/nwops/puppet-debugger
Then install the debug module, include it in your fixtures or just ensure it is in your module path.
https://forge.puppet.com/nwops/debug
Then just set a breakpoint in your code using debug::break() function.
Ruby Version: 2.0.0
Puppet Version: 4.9.4
Puppet Debugger Version: 0.6.0
Created by: NWOps
Type "exit", "functions", "vars", "krt", "whereami", "facts", "resources", "classes",
"play", "classification", "types", "datatypes", "reset", or "help" for more information.
>> $vars = ['one', 'two', 'three']
=> [
[0] "one",
[1] "two",
[2] "three"
]
>> $vars.each | String $var | {
debug::break()
notify{$var:}
}
From file: puppet_debugger_input20170417-97123-qjwbaj.pp
1: $vars.each | String $var | {
=> 2: debug::break()
3: notify{$var:}
4: }
1:>> $var
=> "one"
2:>> exit
From file: puppet_debugger_input20170417-97123-qjwbaj.pp
1: $vars.each | String $var | {
=> 2: debug::break()
3: notify{$var:}
4: }
1:>> $var
=> "two"
2:>> exit
From file: puppet_debugger_input20170417-97123-qjwbaj.pp
1: $vars.each | String $var | {
=> 2: debug::break()
3: notify{$var:}
4: }
1:>> $var
=> "three"