Adding targets section for configuration

Will add a --target <resource> for each item in a comma separated list to the plan and apply commands

Updated the docs to show the new behavior. If left undefined there is no regression in functionality.

DOCS.md

@@ -124,6 +124,26 @@ pipeline:
     root_dir: some/path/here
 ```
 
+## targets
+You may want to only target a specific list of resources within your terraform code. To achieve this you can specify the `targets` parameter. If left undefined all resources will be planned/applied against as the default behavior. You can define multiple targets with a comma separated list.
+
+```yaml
+pipeline:
+  terraform:
+    image: jmccann/drone-terraform:0.5
+    plan: false
+    targets: aws_security_group.generic_sg, aws_security_group.app_sg
+    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
+````
+
 ## Parallelism
 You may want to limit the number of concurrent operations as Terraform walks its graph.
 If you want to change Terraform's default parallelism (currently equal to 10) then set the `parallelism` parameter.

main.go

@@ -4,8 +4,8 @@ import (
 	"encoding/json"
 	"os"
 
-	"github.com/joho/godotenv"
 	"github.com/Sirupsen/logrus"
+	"github.com/joho/godotenv"
 	"github.com/urfave/cli"
 )
 
@@ -73,6 +73,12 @@ func main() {
 			Name:  "env-file",
 			Usage: "source env file",
 		},
+
+		cli.StringSliceFlag{
+			Name:   "targets",
+			Usage:  "targets to run apply or plan on",
+			EnvVar: "PLUGIN_TARGETS",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -116,6 +122,7 @@ func run(c *cli.Context) error {
 			RoleARN:     c.String("role_arn_to_assume"),
 			RootDir:     c.String("root_dir"),
 			Parallelism: c.Int("parallelism"),
+			Targets:     c.StringSlice("targets"),
 		},
 	}
 

plugin.go

@@ -2,11 +2,11 @@ package main
 
 import (
 	"fmt"
+	"github.com/Sirupsen/logrus"
 	"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/Sirupsen/logrus"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -25,6 +25,7 @@ type (
 		RoleARN     string
 		RootDir     string
 		Parallelism int
+		Targets     []string
 	}
 
 	Remote struct {
@@ -52,9 +53,9 @@ func (p Plugin) Exec() error {
 		commands = append(commands, remoteConfigCommand(remote))
 	}
 	commands = append(commands, getModules())
-	commands = append(commands, planCommand(p.Config.Vars, p.Config.Secrets, p.Config.Parallelism))
+	commands = append(commands, planCommand(p.Config.Vars, p.Config.Secrets, p.Config.Parallelism, p.Config.Targets))
 	if !p.Config.Plan {
-		commands = append(commands, applyCommand(p.Config.Parallelism))
+		commands = append(commands, applyCommand(p.Config.Parallelism, p.Config.Targets))
 	}
 	commands = append(commands, deleteCache())
 
@@ -123,11 +124,15 @@ func getModules() *exec.Cmd {
 	)
 }
 
-func planCommand(variables map[string]string, secrets map[string]string, parallelism int) *exec.Cmd {
+func planCommand(variables map[string]string, secrets map[string]string, parallelism int, targets []string) *exec.Cmd {
 	args := []string{
 		"plan",
 		"-out=plan.tfout",
 	}
+	for _, v := range targets {
+		args = append(args, "--target")
+		args = append(args, fmt.Sprintf("%s", v))
+	}
 	for k, v := range variables {
 		args = append(args, "-var")
 		args = append(args, fmt.Sprintf("%s=%s", k, v))
@@ -145,10 +150,14 @@ func planCommand(variables map[string]string, secrets map[string]string, paralle
 	)
 }
 
-func applyCommand(parallelism int) *exec.Cmd {
+func applyCommand(parallelism int, targets []string) *exec.Cmd {
 	args := []string{
 		"apply",
 	}
+	for _, v := range targets {
+		args = append(args, "--target")
+		args = append(args, fmt.Sprintf("%s", v))
+	}
 	if parallelism > 0 {
 		args = append(args, fmt.Sprintf("-parallelism=%d", parallelism))
 	}