Added tf_data_dir parameter and changed plugin to respect TF_DATA_DIR

This commit will enable the plugin to do parallel builds.
The first change is to use Terraform's TF_DATA_DIR environment variable to change the state directory so they will not conflict each other in parallel executions
The second change is to change the plan's output to a different file so they will not be overriden by another parallel execution

main.go

@@ -108,6 +108,11 @@ func main() {
 			Usage:  "a list of var files to use. Each value is passed as -var-file=<value>",
 			EnvVar: "PLUGIN_VAR_FILES",
 		},
+		cli.StringSliceFlag{
+			Name:   "tf_data_dir",
+			Usage:  "changes the location where Terraform keeps its per-working-directory data, such as the current remote backend configuration.",
+			EnvVar: "PLUGIN_TF_DATA_DIR",
+		},
 	}
 
 	if err := app.Run(os.Args); err != nil {
@@ -156,6 +161,7 @@ func run(c *cli.Context) error {
 			Parallelism:      c.Int("parallelism"),
 			Targets:          c.StringSlice("targets"),
 			VarFiles:         c.StringSlice("var_files"),
+			TerraformDataDir: c.String("tf_data_dir"),
 		},
 		Netrc: Netrc{
 			Login:    c.String("netrc.username"),

plugin.go

@@ -33,6 +33,7 @@ type (
 		Parallelism      int
 		Targets          []string
 		VarFiles         []string
+		TerraformDataDir string
 	}
 
 	// Netrc is credentials for cloning
@@ -96,8 +97,8 @@ func (p Plugin) Exec() error {
 		commands = append(commands, installCaCert(p.Config.Cacert))
 	}
 
-	commands = append(commands, deleteCache())
-	commands = append(commands, initCommand(p.Config.InitOptions))
+	commands = append(commands, deleteCache(p.Config))
+	commands = append(commands, initCommand(p.Config))
 	commands = append(commands, getModules())
 
 	// Add commands listed from Actions
@@ -120,7 +121,7 @@ func (p Plugin) Exec() error {
 		}
 	}
 
-	commands = append(commands, deleteCache())
+	commands = append(commands, deleteCache(p.Config))
 
 	for _, c := range commands {
 		if c.Dir == "" {
@@ -183,11 +184,12 @@ func assumeRole(roleArn string) {
 	os.Setenv("AWS_SESSION_TOKEN", value.SessionToken)
 }
 
-func deleteCache() *exec.Cmd {
+func deleteCache(config Config) *exec.Cmd {
+	terraformDataDir := getTerraformDataDir(config)
 	return exec.Command(
 		"rm",
 		"-rf",
-		".terraform",
+		terraformDataDir,
 	)
 }
 
@@ -198,30 +200,30 @@ func getModules() *exec.Cmd {
 	)
 }
 
-func initCommand(config InitOptions) *exec.Cmd {
+func initCommand(config Config) *exec.Cmd {
 	args := []string{
 		"init",
 	}
 
-	for _, v := range config.BackendConfig {
+	for _, v := range config.InitOptions.BackendConfig {
 		args = append(args, fmt.Sprintf("-backend-config=%s", v))
 	}
 
 	// True is default in TF
-	if config.Lock != nil {
-		args = append(args, fmt.Sprintf("-lock=%t", *config.Lock))
+	if config.InitOptions.Lock != nil {
+		args = append(args, fmt.Sprintf("-lock=%t", *config.InitOptions.Lock))
 	}
 
 	// "0s" is default in TF
-	if config.LockTimeout != "" {
-		args = append(args, fmt.Sprintf("-lock-timeout=%s", config.LockTimeout))
+	if config.InitOptions.LockTimeout != "" {
+		args = append(args, fmt.Sprintf("-lock-timeout=%s", config.InitOptions.LockTimeout))
 	}
 
 	// Fail Terraform execution on prompt
 	args = append(args, "-input=false")
 
-	return exec.Command(
-		"terraform",
+	return createTerraformCommand(
+		config,
 		args...,
 	)
 }
@@ -253,9 +255,10 @@ func tfApply(config Config) *exec.Cmd {
 	if config.InitOptions.LockTimeout != "" {
 		args = append(args, fmt.Sprintf("-lock-timeout=%s", config.InitOptions.LockTimeout))
 	}
-	args = append(args, "plan.tfout")
-	return exec.Command(
-		"terraform",
+	args = append(args, getTfoutPath(config))
+
+	return createTerraformCommand(
+		config,
 		args...,
 	)
 }
@@ -279,8 +282,8 @@ func tfDestroy(config Config) *exec.Cmd {
 		args = append(args, fmt.Sprintf("-lock-timeout=%s", config.InitOptions.LockTimeout))
 	}
 	args = append(args, "-force")
-	return exec.Command(
-		"terraform",
+	return createTerraformCommand(
+		config,
 		args...,
 	)
 }
@@ -293,7 +296,7 @@ func tfPlan(config Config, destroy bool) *exec.Cmd {
 	if destroy {
 		args = append(args, "-destroy")
 	} else {
-		args = append(args, "-out=plan.tfout")
+		args = append(args, fmt.Sprintf("-out=%s", getTfoutPath(config)))
 	}
 
 	for _, v := range config.Targets {
@@ -310,8 +313,8 @@ func tfPlan(config Config, destroy bool) *exec.Cmd {
 	if config.InitOptions.LockTimeout != "" {
 		args = append(args, fmt.Sprintf("-lock-timeout=%s", config.InitOptions.LockTimeout))
 	}
-	return exec.Command(
-		"terraform",
+	return createTerraformCommand(
+		config,
 		args...,
 	)
 }
@@ -326,8 +329,8 @@ func tfValidate(config Config) *exec.Cmd {
 	for k, v := range config.Vars {
 		args = append(args, "-var", fmt.Sprintf("%s=%s", k, v))
 	}
-	return exec.Command(
-		"terraform",
+	return createTerraformCommand(
+		config,
 		args...,
 	)
 }
@@ -348,12 +351,49 @@ func tfFmt(config Config) *exec.Cmd {
 	if config.FmtOptions.Check != nil {
 		args = append(args, fmt.Sprintf("-check=%t", *config.FmtOptions.Check))
 	}
-	return exec.Command(
-		"terraform",
+	return createTerraformCommand(
+		config,
 		args...,
 	)
 }
 
+func getTerraformDataDir(config Config) string {
+	// Override terraform data dir
+	var terraformDataDir string
+	if config.TerraformDataDir != "" {
+		terraformDataDir = config.TerraformDataDir
+	} else if os.Getenv("TF_DATA_DIR") != "" {
+		terraformDataDir = os.Getenv("TF_DATA_DIR")
+	} else {
+		terraformDataDir = ".terraform"
+	}
+	return terraformDataDir
+}
+
+func createEnvironmentVariables(config Config) []string {
+	var environmentVariables []string = []string{}
+
+	terraformDataDir := getTerraformDataDir(config)
+	if terraformDataDir != ".terraform" {
+		environmentVariables = append(environmentVariables, fmt.Sprintf("TF_DATA_DIR=%s", terraformDataDir))
+	}
+	return environmentVariables
+}
+
+func createTerraformCommand(config Config, args ...string) *exec.Cmd {
+	command := exec.Command("terraform", args...)
+	command.Env = append(command.Env, createEnvironmentVariables(config)...)
+	return command
+}
+func getTfoutPath(config Config) string {
+	terraformDataDir := getTerraformDataDir(config)
+	if terraformDataDir == ".terraform" {
+		return "plan.tfout"
+	} else {
+		return fmt.Sprintf("%s.plan.tfout", terraformDataDir)
+	}
+}
+
 func vars(vs map[string]string) []string {
 	var args []string
 	for k, v := range vs {

plugin_test.go

@@ -204,4 +204,59 @@ func TestPlugin(t *testing.T) {
 			}
 		})
 	})
+
+	g.Describe("tfDataDir", func() {
+		g.It("Should override the terraform data dir environment variable when provided", func() {
+			type args struct {
+				config Config
+			}
+
+			tests := []struct {
+				name            string
+				args            args
+				want            *exec.Cmd
+				expectedEnvVars []string
+			}{
+				{
+					"with TerraformDataDir",
+					args{config: Config{TerraformDataDir: ".overriden_terraform_dir"}},
+					exec.Command("terraform", "apply", ".overriden_terraform_dir.plan.tfout"),
+					[]string{"TF_DATA_DIR=.overriden_terraform_dir"},
+				},
+				{
+					"with TerraformDataDir value as .terraform",
+					args{config: Config{TerraformDataDir: ".terraform"}},
+					exec.Command("terraform", "apply", "plan.tfout"),
+					[]string{},
+				},
+				{
+					"without TerraformDataDir",
+					args{config: Config{}},
+					exec.Command("terraform", "apply", "plan.tfout"),
+					[]string{},
+				},
+			}
+
+			for _, tt := range tests {
+				applied := tfApply(tt.args.config)
+				appliedEnv := applied.Env
+				applied.Env = nil
+
+				g.Assert(applied).Equal(tt.want)
+
+				var found int = 0
+
+				for _, expectedEnvVar := range tt.expectedEnvVars {
+					for _, env := range appliedEnv {
+						if expectedEnvVar == env {
+							found += 1
+							break
+						}
+					}
+				}
+				g.Assert(found).Equal(len(tt.expectedEnvVars))
+
+			}
+		})
+	})
 }