debugging-with-delve.md

Debugging with Delve

In the past, the only way to know what was happening in Terraform was to drop something like this around your code.

log.Println("[DEBUG] Something happened!")
// or
tflog.Debug(ctx, fmt.Sprintf("broken thing: %#v", thing))

This is incredibly tedious, and you end up wasting time going back and forth on what you want to inspect and in what states.

Since we've finally upgraded to terraform-plugin-sdk v2, we're able to advance from log based debugging with Terraform to using a debugger. My choice for Golang is Delve however some Gophers will favour gdb instead.

Below, I'm using VS Code as my editor however should be able to sub in your editor equivalent and follow along.

• Drop into a terminal session

• Clone the git repository into your Go directory

  $ git clone git@github.com:cloudflare/terraform-provider-cloudflare.git /Users/jacob/go/src/github.com/cloudflare/
  

• Build the development version of the provider binary. It is important to use the development version to disable compiler optimisations and inlining; without these compile flags some parts of Delve just won't work.

  $ make build-dev
  

• Once the build finishes, confirm the binary exists

  $ file terraform-provider-cloudflare_99.0.0
    terraform-provider-cloudflare_99.0.0: Mach-O 64-bit executable x86_64
  

• Now that the binary is created, you can execute Delve in headless mode. I use a static listen address here to make the debugging configuration consistent but you can also use the ephemeral port assigned if you'd rather do that.

  $ dlv exec --headless ./terraform-provider-cloudflare_99.0.0 --listen 127.0.0.1:44444 -- --debug
  API server listening at: 127.0.0.1:44444
  debugserver-@(#)PROGRAM:LLDB  PROJECT:lldb-1300.0.32.2
    for x86_64.
  Got a connection, launched process ./terraform-provider-cloudflare_99.0.0 (pid = 92684).
  

  Be sure to leave this window/tab open. It will soon have an environment variable configuration for you to prefix your Terraform commands with.

• In VS Code, create a new launch.json for debugging. Drop in the following snippet.

  {
    "version": "0.2.0",
    "configurations": [
      {
        "name": "Terraform delve debugger",
        "type": "go",
        "request": "attach",
        "mode": "remote",
        "remotePath": "${workspaceFolder}",
        "port": 44444,
        "host": "127.0.0.1",
        "apiVersion": 1.0
      }
    ]
  }

• You can now hit the "start debugger" button in VS code.

  

• If you've done everything correct up until this point, you should now be able to pop back to the Delve terminal session and see it has now output a TF_REATTACH_PROVIDERS configuration below your dlv exec command.

  {"@level":"debug","@message":"plugin address","@timestamp":"2021-09-23T13:56:14.703121+10:00","address":"/var/folders/36/zlscnhfn27n1yxx52cr1kdmr0000gp/T/plugin1090848880","network":"unix"}
  Provider started, to attach Terraform set the TF_REATTACH_PROVIDERS env var:
  
    TF_REATTACH_PROVIDERS='{"registry.terraform.io/cloudflare/cloudflare":{"Protocol":"grpc","ProtocolVersion":5,"Pid":92684,"Test":true,"Addr":{"Network":"unix","String":"/var/folders/36/zlscnhfn27n1yxx52cr1kdmr0000gp/T/plugin1090848880"}}}'
  
  {"@level":"debug","@message":"stdio EOF, exiting copy loop","@timestamp":"2021-09-23T13:58:24.698711+10:00"}
  {"@level":"debug","@message":"stdio EOF, exiting copy loop","@timestamp":"2021-09-23T13:58:24.698712+10:00"}
  

• Now, it is just a matter of prefixing your Terraform commands (apply/plan, go tests) with this environment variable and it will hit the breakpoints you've set. You can also export this into the environment if you'd rather instead of prefixing all commands.

  $ TF_REATTACH_PROVIDERS='{"registry.terraform.io/cloudflare/cloudflare":{"Protocol":"grpc","ProtocolVersion":5,"Pid":92684,"Test":true,"Addr":{"Network":"unix","String":"/var/folders/36/zlscnhfn27n1yxx52cr1kdmr0000gp/T/plugin1090848880"}}}' \
    CLOUDFLARE_EMAIL="..." CLOUDFLARE_API_KEY="..." terraform apply