Extending a Terraform Provider

Problem #

At my day job we use terraform pretty extensively for all of our infrastructure. We also use terraform along with some other automations to automatically create dashboards and monitors for new teams and services.

Starting point #

Hashicorp provides an excellent tutorial on their learning site on how to write a provider for terraform. Datadog also has some useful instructions on the development process they use for this provider.

Here is the PR that adds the ability to create a monitor using a JSON document.

Forcing in dev provider #

To not use the provider from the registry and instead use a local one under development, create a config file for the terraform cli:

provider_installation {  
  dev_overrides {
  	# provider to be overridden, path to new provider.
	# path must include provider binary with name as it is expected appear
	# e.g. terraform-provider-datadog
    "<repository>/<provider-name>" = "/Users/<username>/go/bin/"
	"Datadog/datadog" = "/Users/spothier/go/github.com/Datadog/datadog-terraformprovider"
 }  
  direct {}  
}

Force the cli to use this config with TF_CLI_CONFIG_FILE=/path/to/dev.tfrc

https://www.terraform.io/docs/cli/config/config-file.html#development-overrides-for-provider-developers

Debugging #

Add the following to main.go and run with --debug flag:

func main() {
    var debugMode bool

    flag.BoolVar(&debugMode, "debug", false, "set to true to run the provider with support for debuggers like delve")
    flag.Parse()

    opts := &plugin.ServeOpts{ProviderFunc: provider.New}

    if debugMode {
        // TODO: update this string with the full name of your provider as used in your configs
        err := plugin.Debug(context.Background(), "registry.terraform.io/my-org/my-provider", opts)
        if err != nil {
            log.Fatal(err.Error())
        }
        return
    }

    plugin.Serve(opts)
}

This will output something like:

TF_REATTACH_PROVIDERS='{"registry.terraform.io/my-org/my-provider":{"Protocol":"grpc","ProtocolVersion":5,"Pid":26460,"Test":true,"Addr":{"Network":"unix","String":"/var/folders/y8/bxwjmbw535n429n5nb7b86y80000gp/T/plugin216655400"}}}'

Add/export this when running terraform plan/apply and it will use the running provider

https://www.terraform.io/docs/extend/debugging.html#enabling-debugging-in-a-provider