Allow for more flexibility in ConfigMap with config template file defaults.

Prior to this change, a single configuration file customization required
updating every file in the ConfigMap.

This change allows for individual configuration files to be updated, and
defaults back to the default configuration files if the updated configuration
file is not present.

Author: Conor.Quin <[email protected]> @Conor-Quin
Author: Jonathan S. Katz <[email protected]> @jkatz

Author: Conor-Quin

config/pgoconfig.go

@@ -820,29 +820,53 @@ func getRootPath(clientset *kubernetes.Clientset, namespace string) (*v1.ConfigM
 // LoadTemplate will load a JSON template from a path
 func (c *PgoConfig) LoadTemplate(cMap *v1.ConfigMap, rootPath, path string) (*template.Template, error) {
 	var value string
+	var err error
 
+	// Determine if there exists a configmap entry for the template file.
 	if cMap != nil {
+		// Get the data that is stored in the configmap
 		value = cMap.Data[path]
-		if value == "" {
-			errMsg := fmt.Sprintf("%s path not found in ConfigMap", path)
-			return nil, errors.New(errMsg)
-		}
-	} else {
-		fullPath := rootPath + path
-		log.Debugf("loading path [%s]", fullPath)
-		buf, err := ioutil.ReadFile(fullPath)
+	}
+
+	// if the configmap does not exist, or there is no data in the configmap for
+	// this particular configuration template, attempt to load the template from
+	// the default configuration
+	if cMap == nil || value == "" {
+		value, err = c.DefaultTemplate(path)
+
 		if err != nil {
-			log.Errorf("error: could not read %s", fullPath)
-			log.Error(err)
 			return nil, err
 		}
-		value = string(buf)
 	}
 
+	// if we have a value for the templated file, return
 	return template.Must(template.New(path).Parse(value)), nil
 
 }
 
+// DefaultTemplate attempts to load a default configuration template file
+func (c *PgoConfig) DefaultTemplate(path string) (string, error) {
+	// set the lookup value for the file path based on the default configuration
+	// path and the template file requested to be loaded
+	fullPath := DefaultConfigsPath + path
+
+	log.Debugf("No entry in cmap loading default path [%s]", fullPath)
+
+	// read in the file from the default path
+	buf, err := ioutil.ReadFile(fullPath)
+
+	if err != nil {
+		log.Errorf("error: could not read %s", fullPath)
+		log.Error(err)
+		return "", err
+	}
+
+	// extract the value of the default configuration file and return
+	value := string(buf)
+
+	return value, nil
+}
+
 func (c *PgoConfig) SetDefaultStorageClass(clientset *kubernetes.Clientset) error {
 
 	selector := LABEL_PGO_DEFAULT_SC + "=true"