diff --git a/library/Director/CustomVariable/CustomVariable.php b/library/Director/CustomVariable/CustomVariable.php
index d78fcb75..2d0761b8 100644
--- a/library/Director/CustomVariable/CustomVariable.php
+++ b/library/Director/CustomVariable/CustomVariable.php
@@ -67,6 +67,15 @@ abstract class CustomVariable implements IcingaConfigRenderer
         return $this->getValue();
     }
 
+    public function toJson()
+    {
+        if ($this->getDbFormat() === 'string') {
+            return json_encode($this->getDbValue());
+        } else {
+            return $this->getDbValue();
+        }
+    }
+
     // TODO: abstract
     public function getDbFormat()
     {
@@ -91,6 +100,34 @@ abstract class CustomVariable implements IcingaConfigRenderer
         );
     }
 
+    public function flatten(array & $flat, $prefix)
+    {
+        $flat[$prefix] = $this->getDbValue();
+    }
+
+    public function render($renderExpressions = false)
+    {
+        return c::renderKeyValue(
+            $this->renderKeyName($this->getKey()),
+            $this->toConfigStringPrefetchable($renderExpressions)
+        );
+    }
+
+    protected function renderKeyName($key)
+    {
+        if (preg_match('/^[a-z0-9_]+\d*$/i', $key)) {
+            return 'vars.' . c::escapeIfReserved($key);
+        } else {
+            return 'vars[' . c::renderString($key) . ']';
+        }
+    }
+
+    public function checksum()
+    {
+        // TODO: remember checksum, invalidate on change
+        return sha1($this->getKey() . '=' . $this->toJson(), true);
+    }
+
     public function isNew()
     {
         return ! $this->loadedFromDb;
diff --git a/library/Director/CustomVariable/CustomVariableArray.php b/library/Director/CustomVariable/CustomVariableArray.php
index da9a624c..c5428ba1 100644
--- a/library/Director/CustomVariable/CustomVariableArray.php
+++ b/library/Director/CustomVariable/CustomVariableArray.php
@@ -69,6 +69,13 @@ class CustomVariableArray extends CustomVariable
         return $this;
     }
 
+    public function flatten(array & $flat, $prefix)
+    {
+        foreach ($this->value as $k => $v) {
+            $v->flatten($flat, sprintf('%s[%d]', $prefix, $k));
+        }
+    }
+
     public function toConfigString($renderExpressions = false)
     {
         $parts = array();
diff --git a/library/Director/CustomVariable/CustomVariableDictionary.php b/library/Director/CustomVariable/CustomVariableDictionary.php
index cd101290..c5ce7bda 100644
--- a/library/Director/CustomVariable/CustomVariableDictionary.php
+++ b/library/Director/CustomVariable/CustomVariableDictionary.php
@@ -75,6 +75,13 @@ class CustomVariableDictionary extends CustomVariable implements Countable
         return $ret;
     }
 
+    public function flatten(array & $flat, $prefix)
+    {
+        foreach ($this->value as $k => $v) {
+            $v->flatten($flat, sprintf('%s["%s"]', $prefix, $k));
+        }
+    }
+
     public function listKeys()
     {
         $keys = array_keys($this->value);
diff --git a/library/Director/CustomVariable/CustomVariableString.php b/library/Director/CustomVariable/CustomVariableString.php
index cbc5bc6d..530ca4ce 100644
--- a/library/Director/CustomVariable/CustomVariableString.php
+++ b/library/Director/CustomVariable/CustomVariableString.php
@@ -37,6 +37,12 @@ class CustomVariableString extends CustomVariable
         return $this;
     }
 
+    public function flatten(array & $flat, $prefix)
+    {
+        // TODO: we should get rid of type=string and always use JSON
+        $flat[$prefix] = json_encode($this->getValue());
+    }
+
     public function toConfigString($renderExpressions = false)
     {
         if ($renderExpressions) {
diff --git a/library/Director/CustomVariable/CustomVariables.php b/library/Director/CustomVariable/CustomVariables.php
index 05e10933..4275c50b 100644
--- a/library/Director/CustomVariable/CustomVariables.php
+++ b/library/Director/CustomVariable/CustomVariables.php
@@ -273,6 +273,26 @@ class CustomVariables implements Iterator, Countable, IcingaConfigRenderer
         return $this->storedVars;
     }
 
+    public function flatten()
+    {
+        $flat = array();
+        foreach ($this->vars as $key => $var) {
+            $var->flatten($flat, $key);
+        }
+
+        return $flat;
+    }
+
+    public function checksum()
+    {
+        $sums = array();
+        foreach ($this->vars as $key => $var) {
+            $sums[] = $key . '=' . $var->checksum();
+        }
+
+        return sha1(implode('|', $sums), true);
+    }
+
     public function toConfigString($renderExpressions = false)
     {
         $out = '';