diff --git a/flamingo/services/alias_engine.py b/flamingo/services/alias_engine.py
index 21fc20e..c9a147d 100644
--- a/flamingo/services/alias_engine.py
+++ b/flamingo/services/alias_engine.py
@@ -1,4 +1,6 @@
 import logging
+import re
+from dataclasses import field, dataclass
 from typing import Generator, Any, Tuple
 
 from sanic_rest.exceptions import ValidationError
@@ -8,17 +10,50 @@
 logger = logging.getLogger()
 
 
+ALIAS_REGEX = r"\${(?P<alias_to>.*)}"
+
+
+@dataclass
+class ReplacementEngine:
+    replacements: KeyValue = field(default_factory=dict)
+
+    def add(self, items: KeyValue):
+        for k, v in items.items():
+            if AliasEngine.is_virtual(value=v):
+                continue
+            self.replacements[k] = v
+
+    def get(self, value):
+        return self.replacements[value]
+
+    def replace(self, virtual_value):
+        alias_to = re.match(ALIAS_REGEX, virtual_value).group('alias_to')
+
+        try:
+            replace_with = self.replacements[alias_to]
+        except KeyError as e:
+            raise ValidationError(f"Could not find the referenced env var for {virtual_value.as_kv}") from e
+
+        return re.sub(ALIAS_REGEX, replace_with, virtual_value)
+
+
 class AliasEngine:
-    def __init__(self, items: KeyValue, replacements: KeyValue = None):
+    def __init__(self, items: KeyValue, replacements: ReplacementEngine = None):
         super().__init__()
         self._concrete: KeyValue = dict()
         self._virtual: KeyValue = dict()
-        self._replacements: KeyValue = replacements or items
+
+        if not replacements:
+            replacements = ReplacementEngine()
+            replacements.add(items=items)
+        self._replacements = replacements
 
         self.extend(items)
 
-    def is_virtual(self, value):
-        return False  # TODO We need an use case for this, the syntax must not be defined too
+    @classmethod
+    def is_virtual(cls, value):
+        matches = re.match(ALIAS_REGEX, str(value))
+        return bool(matches)
 
     def append(self, key: str, value: Any) -> None:
         container = self._virtual if self.is_virtual(value) else self._concrete
@@ -33,14 +68,4 @@ def extend(self, items: KeyValue) -> None:
     def items(self) -> Generator[Tuple[str, Any], None, None]:
         yield from self._concrete.items()
         for key, virtual_value in self._virtual.items():
-            yield key, self._to_concrete(virtual_value=virtual_value)
-
-    def _to_concrete(self, virtual_value) -> Any:
-        alias_to = virtual_value[1:]
-
-        try:
-            value = self._replacements[alias_to]
-        except KeyError as e:
-            raise ValidationError(f"Could not find the referenced env var for {virtual_value.as_kv}") from e
-
-        return value
+            yield key, self._replacements.replace(virtual_value=virtual_value)
diff --git a/flamingo/services/builders.py b/flamingo/services/builders.py
index d2aadd8..134b47c 100644
--- a/flamingo/services/builders.py
+++ b/flamingo/services/builders.py
@@ -6,15 +6,13 @@
 from gcp_pilot.build import CloudBuild, Substitutions
 from gcp_pilot.exceptions import NotFound
 from gcp_pilot.run import CloudRun
-from gcp_pilot.dns import CloudDNS, RecordType
 from google.cloud.devtools import cloudbuild_v1
 
-import settings
 from models.app import App
 from models.base import KeyValue
 from models.buildpack import Target
 from models.schedule import ScheduledInvocation
-from services.alias_engine import AliasEngine
+from services.alias_engine import AliasEngine, ReplacementEngine
 
 logger = logging.getLogger()
 
@@ -63,10 +61,10 @@ def _get_env_and_build_args(self) -> Tuple[KeyValue, KeyValue]:
         all_env_vars = {var.key: var.value for var in self.app.get_all_env_vars()}
         all_build_args = self.app.get_all_build_args()
 
-        replacements = dict()
-        replacements.update(self._setup_params)
-        replacements.update(all_env_vars)
-        replacements.update(all_build_args)
+        replacements = ReplacementEngine()
+        replacements.add(items=self._setup_params)
+        replacements.add(items=all_env_vars)
+        replacements.add(items=all_build_args)
 
         env_var_engine = AliasEngine(
             items=all_env_vars,