diff --git a/Provision/Config.php b/Provision/Config.php
index 763b003..130aa4d 100644
--- a/Provision/Config.php
+++ b/Provision/Config.php
@@ -167,6 +167,10 @@ class Provision_Config {
    * array.
    */
   private function render_template($template, $variables) {
+    
+    // Allow modules to alter the variables before writing to the template.
+    // @see hook_provision_config_variables_alter()
+    drush_command_invoke_all_ref('provision_config_variables_alter', $variables, $template, $this);
     drush_errors_off();
     extract($variables, EXTR_SKIP);  // Extract the variables to a local namespace
     ob_start();                      // Start output buffering
diff --git a/provision.api.php b/provision.api.php
index 3f491ff..855f9cf 100644
--- a/provision.api.php
+++ b/provision.api.php
@@ -216,6 +216,31 @@ function hook_provision_config_load_templates_alter(&$templates, $config) {
 }
 
 /**
+ * Alter the template and variables used for rendering a config file.
+ *
+ * When implementing this hook, the function name should start with your file's name, not "drush_".
+ *
+ * @param $variables
+ *   The variables that are about to be injected into the template.
+ * @param $template
+ *   The template file chosen for use
+ * @param $config
+ *   The Provision_config object trying to find its template.
+ *
+ * @see hook_provision_config_load_templates()
+ * @see hook_provision_config_load_templates_alter()
+ */
+function hook_provision_config_variables_alter(&$variables, $templates, $config) {
+  
+  // If this is the vhost template and the http service is Docker...
+  if (is_a($config, 'Provision_Config_Apache_Site') && is_a(d()->platform->service('http'), 'Provision_Service_http_apache_docker')) {
+    
+    // Force the listen port to be 80.
+    $variables['http_port'] = '80';
+  }
+}
+
+/**
  * Alter the array of directories to create.
  *
  * @param $mkdir