Run terraform from source

[Justin]

I've gotten a basic "make dev" terraform dev env setup however, being new to go, I've had problems invoking terraform using 'go run' or anything of the sort. I really need to step through the execution of a terraform plugin so I can see 'ResourceData' being passed in and out of the plugin and see the Provider() function executed. On top of not knowing how to do this, go lacks anything like 'pdb.set_trace()' which I would really like to be able to dig into this code. Does anyone have any helpful tips? Thanks in advance.

[Sander van Harmelen]

Hi Justin,

If you put `TF_FORK=0` in your env, it should prevent Terraform from forking (re-exec) it’s core binary. So then you should be able to use a debugger like Delve (https://github.com/derekparker/delve) from the command line or use your favourite editor. Unless that is vim/neovim which I use, as those don’t have debugger integration. But Atom, VSCode and Gogland (JetBrains) and likely others I don’t know do have debugging capabilities for debugging Go built into their products.

One issue you will still have is that plugins are spawn in their own process. Even if they are builtin providers, they will be started in their own process by calling the `terraform` binary with a few specific parameters which will launch the plugin instead of the core binary itself. Maybe this sounds a bit fuzzy, but without going through all the nitty gritty details this is the easiest way to describe how things work.

So it should be fairly easy to debug Terraform core, but it will be harder to debug plugins by using a debugger. I myself got used to not use a debugger since I'm working almost exclusively in Go for a few years now. Just adding some `log.Printf` statements in the right places or `pretty.Print` (https://github.com/kr/pretty) more then often does the job just as well… 

Sander

On 30 May 2017, at 09:47: 05, Justin <justinp...@gmail.com> wrote:

I've gotten a basic "make dev" terraform dev env setup however, being new to go, I've had problems invoking terraform using 'go run' or anything of the sort. I really need to step through the execution of a terraform plugin so I can see 'ResourceData' being passed in and out of the plugin and see the Provider() function executed. On top of not knowing how to do this, go lacks anything like 'pdb.set_trace()' which I would really like to be able to dig into this code. Does anyone have any helpful tips? Thanks in advance.

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[Justin]

Thanks Sander, 

Thanks to you I can now step through terraform core with delve and I have also followed the advice of https://www.terraform.io/docs/internals/debugging.html However, I'm still curious how to actually step through the provider code with a debugger. I understand how the providers are called but does anyone here actually have a working setup of tracing (with a debugger) through their provider code? My worry with delve is that in order to prevent trashing it locks you into one goroutine and that it may be quite difficult to step into the provider execution path. 

Sander

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[Sander van Harmelen]

Not sure if this will work, but I think it’s the only way to achieve your goal… If you set a breakpoint in the core binary right after the call to initialise a new provider, that would cause the execution to be paused and gives you some time to connect Delve to the newly spawn process (dlv attach pid). You would then have 2 delve sessions to both the core binary and the spawned provider…

Cheers,

Sander

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