diff --git a/static/directives/config/config-setup-tool.html b/static/directives/config/config-setup-tool.html
index a2c3c0fad..2c8397ecb 100644
--- a/static/directives/config/config-setup-tool.html
+++ b/static/directives/config/config-setup-tool.html
@@ -62,7 +62,7 @@
             <td>
               <span class="config-string-field" binding="config.SERVER_HOSTNAME"
                     placeholder="Hostname (and optional port if non-standard)"
-                    pattern="^[a-zA-Z-0-9\.]+(:[0-9]+)?$"></span>
+                    pattern="{{ HOSTNAME_REGEX }}"></span>
               <div class="help-text">
                  The HTTP host (and optionally the port number if a non-standard HTTP/HTTPS port) of the location
                   where the registry will be accessible on the network
@@ -121,7 +121,8 @@
             <td>
               <span class="config-string-field" binding="mapped.redis.host"
                     placeholder="The redis server hostname"
-                    pattern="^[a-zA-Z-0-9\.]+(:[0-9]+)?$"></span>
+                    pattern="{{ HOSTNAME_REGEX }}"
+                    validator="validateHostname(value)">></span>
             </td>
           </tr>
           <tr>
@@ -216,7 +217,8 @@
             <td>
               <span class="config-string-field" binding="config.MAIL_SERVER"
                     placeholder="SMTP server for sending e-mail"
-                    pattern="^[a-zA-Z-0-9\.]+(:[0-9]+)?$"></span>
+                    pattern="{{ HOSTNAME_REGEX }}"
+                    validator="validateHostname(value)">></span>
             </td>
           </tr>
           <tr>
@@ -377,7 +379,7 @@
               <span class="config-string-field"
                     binding="config.GITHUB_LOGIN_CONFIG.GITHUB_ENDPOINT"
                     placeholder="https://my.githubserver"
-                    pattern="^https?://([a-zA-Z0-9]+\.?\/?)+$">
+                    pattern="{{ GITHUB_REGEX }}">
               </span>
               <div class="help-text">
                 The Github Enterprise endpoint. Must start with http:// or https://.
@@ -509,7 +511,7 @@
               <span class="config-string-field"
                     binding="config.GITHUB_TRIGGER_CONFIG.GITHUB_ENDPOINT"
                     placeholder="https://my.githubserver"
-                    pattern="^https?://([a-zA-Z0-9]+\.?\/?)+$">
+                    pattern="{{ GITHUB_REGEX }}">
               </span>
               <div class="help-text">
                 The Github Enterprise endpoint. Must start with http:// or https://.
diff --git a/static/directives/config/config-string-field.html b/static/directives/config/config-string-field.html
index 5cbbe8a35..7714fd541 100644
--- a/static/directives/config/config-string-field.html
+++ b/static/directives/config/config-string-field.html
@@ -3,5 +3,8 @@
     <input type="text" class="form-control" placeholder="{{ placeholder || '' }}"
            ng-model="binding" ng-trim="false" ng-minlength="1"
            ng-pattern="getRegexp(pattern)" required>
+    <div class="alert alert-danger" ng-show="errorMessage">
+        {{ errorMessage }}
+    </div>
   </form>
 </div>
diff --git a/static/js/core-config-setup.js b/static/js/core-config-setup.js
index e6a79d4b6..0b1f42e62 100644
--- a/static/js/core-config-setup.js
+++ b/static/js/core-config-setup.js
@@ -10,6 +10,9 @@ angular.module("core-config-setup", ['angularFileUpload'])
         'isActive': '=isActive'
       },
       controller: function($rootScope, $scope, $element, $timeout, ApiService) {
+        $scope.HOSTNAME_REGEX = '^[a-zA-Z-0-9\.]+(:[0-9]+)?$';
+        $scope.GITHUB_REGEX = '^https?://([a-zA-Z0-9]+\.?\/?)+$';
+
         $scope.SERVICES = [
           {'id': 'redis', 'title': 'Redis'},
 
@@ -69,6 +72,14 @@ angular.module("core-config-setup", ['angularFileUpload'])
           ]
         };
 
+        $scope.validateHostname = function(hostname) {
+          if (hostname.indexOf('127.0.0.1') == 0 || hostname.indexOf('localhost') == 0) {
+            return 'Please specify a non-localhost hostname. "localhost" will refer to the container, not your machine.'
+          }
+
+          return null;
+        };
+
         $scope.config = null;
         $scope.mapped = {
           '$hasChanges': false
@@ -719,7 +730,8 @@ angular.module("core-config-setup", ['angularFileUpload'])
         'binding': '=binding',
         'placeholder': '@placeholder',
         'pattern': '@pattern',
-        'defaultValue': '@defaultValue'
+        'defaultValue': '@defaultValue',
+        'validator': '&validator'
       },
       controller: function($scope, $element) {
         $scope.getRegexp = function(pattern) {
@@ -733,6 +745,8 @@ angular.module("core-config-setup", ['angularFileUpload'])
           if (!binding && $scope.defaultValue) {
             $scope.binding = $scope.defaultValue;
           }
+
+          $scope.errorMessage = $scope.validator({'value': binding || ''});
         });
       }
     };