feat: implement heroku's postdeploy deployment task

This occurs during the postdeploy on the first deploy of an app, mimicking heroku. It currently happens _after_ the `postdeploy` and `release` deploy tasks.

plugins/app-json/triggers.go

@@ -1,6 +1,7 @@
 package appjson
 
 import (
+	"fmt"
 	"os"
 	"path/filepath"
 
@@ -9,16 +10,16 @@ import (
 
 // TriggerInstall initializes app restart policies
 func TriggerInstall() error {
+	if err := common.PropertySetup("common"); err != nil {
+		return fmt.Errorf("Unable to install the common plugin: %s", err.Error())
+	}
+
 	directory := filepath.Join(common.MustGetEnv("DOKKU_LIB_ROOT"), "data", "app-json")
 	if err := os.MkdirAll(directory, 0755); err != nil {
 		return err
 	}
 
-	if err := common.SetPermissions(directory, 0755); err != nil {
-		return err
-	}
-
-	return nil
+	return common.SetPermissions(directory, 0755)
 }
 
 // TriggerPostDelete destroys the app-json data for a given app container
@@ -41,10 +42,7 @@ func TriggerPostDeploy(appName string, imageTag string) error {
 		return err
 	}
 
-	if err := executeScript(appName, image, imageTag, "postdeploy"); err != nil {
-		return err
-	}
-	return nil
+	return executeScript(appName, image, imageTag, "postdeploy")
 }
 
 // TriggerPreDeploy is a trigger to execute predeploy and release deployment tasks
@@ -65,5 +63,19 @@ func TriggerPreDeploy(appName string, imageTag string) error {
 	if err := executeScript(appName, image, imageTag, "release"); err != nil {
 		return err
 	}
-	return nil
+
+	if common.PropertyGet("common", appName, "deployed") == "true" {
+		return nil
+	}
+
+	// Ensure that a failed postdeploy does not trigger twice
+	if common.PropertyGet("app-json", appName, "heroku.postdeploy") == "executed" {
+		return nil
+	}
+
+	if err := common.PropertyWrite("app-json", appName, "heroku.postdeploy", "executed"); err != nil {
+		return err
+	}
+
+	return executeScript(appName, image, imageTag, "heroku.postdeploy")
 }