adding ability to change root dir for commands

Conflicts:
	main.go

DOCS.md

@@ -9,6 +9,7 @@ Use the Terraform plugin to apply the infrastructure configuration contained wit
 * `ca_cert` - ca cert to add to your environment to allow terraform to use internal/private resources
 * `sensitive` (default: `false`) - Whether or not to suppress terraform commands to stdout.
 * `role_arn_to_assume` - A role to assume before running the terraform commands
+* `root_dir` - The root directory where the terraform files live. When unset, the top level directory will be assumed.
 
 The following is a sample Terraform configuration in your .drone.yml file:
 
@@ -93,3 +94,22 @@ deploy:
       app_version: 1.0.0
     role_arn_to_assume: arn:aws:iam::account-of-role-to-assume:role/name-of-role
 ```
+
+## Root dir
+You may want to change directories before applying the terraform commands.  This parameter is useful if you have multiple environments in different folders and you want to use different drone configurations to apply different environments.
+
+```yaml
+deploy:
+  terraform:
+    plan: false
+    remote:
+      backend: S3
+      config:
+        bucket: my-terraform-config-bucket
+        key: tf-states/my-project
+        region: us-east-1
+    vars:
+      app_name: my-project
+      app_version: 1.0.0
+    root_dir: some/path/here
+```

main.go

@@ -2,16 +2,16 @@ package main
 
 import (
 	"fmt"
-	"io/ioutil"
-	"os"
-	"os/exec"
-	"strings"
-    "time"
 	"github.com/aws/aws-sdk-go/aws/credentials"
 	"github.com/aws/aws-sdk-go/aws/credentials/stscreds"
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/sts"
 	"github.com/drone/drone-plugin-go/plugin"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"strings"
+	"time"
 )
 
 var (
@@ -25,6 +25,7 @@ type terraform struct {
 	Cacert    string            `json:"ca_cert"`
 	Sensitive bool              `json:"sensitive"`
 	RoleARN   string            `json:"role_arn_to_assume"`
+	RootDir   string            `json:"root_dir"`
 }
 
 type remote struct {
@@ -64,6 +65,9 @@ func main() {
 	for _, c := range commands {
 		c.Env = os.Environ()
 		c.Dir = workspace.Path
+		if vargs.RootDir != "" {
+			c.Dir = c.Dir + "/" + vargs.RootDir
+		}
 		c.Stdout = os.Stdout
 		c.Stderr = os.Stderr
 		if !vargs.Sensitive {