Fail closed when ALLOWED_HOSTS is not set in production

charts/qiskit-serverless/charts/gateway/values.yaml

@@ -73,7 +73,10 @@ application:
   runtimeApi:
     url: "https://quantum.cloud.ibm.com"
     cacheTtl: "1"
-  allowedHosts: "*"
+  # Set this to the host(s) the gateway serves. It is empty by default so a
+  # deployment that forgets to set it fails closed (the gateway refuses to boot)
+  # instead of accepting any Host header. Set "*" only for local development.
+  allowedHosts: ""
   trustedOrigins: "http://localhost"
   corsOrigins: "http://localhost"
   logsMaximumSize: "52428800" # 50Mb in bytes

docker-compose.yaml

@@ -47,6 +47,7 @@ services:
     user: "root" # root user is needed to write on volumes
     environment:
       - DEBUG=0
+      - ALLOWED_HOSTS=*
       # Local-only dev secret. With DEBUG=0 the app fails closed without this.
       - DJANGO_SECRET_KEY=django-insecure-local-compose-only-change-me
       - RAY_HOST=http://ray-head:8265
@@ -78,6 +79,7 @@ services:
     entrypoint: "./entrypoint-scheduler.sh"
     environment:
       - DEBUG=0
+      - ALLOWED_HOSTS=*
       # Local-only dev secret. With DEBUG=0 the app fails closed without this.
       - DJANGO_SECRET_KEY=django-insecure-local-compose-only-change-me
       - DATABASE_HOST=postgres

gateway/main/settings.py

@@ -58,7 +58,17 @@
 LOG_FORMAT = "json" if os.environ.get("LOG_FORMAT", "simple") == "json" else "simple"
 
 # It must be a full url without protocol: mydomain.com
-ALLOWED_HOSTS = os.environ.get("ALLOWED_HOSTS", "*").split(",")
+# Accepting any Host ("*") enables Host header attacks (cache poisoning and
+# password-reset links pointing at an attacker domain). In production (DEBUG off)
+# the process fails closed if ALLOWED_HOSTS is not set, instead of defaulting to
+# a value. A hardcoded "*" is only used for local development and tests.
+_allowed_hosts = os.environ.get("ALLOWED_HOSTS")
+if not _allowed_hosts:
+    if DEBUG or IS_TEST:
+        _allowed_hosts = "*"
+    else:
+        raise ImproperlyConfigured("ALLOWED_HOSTS environment variable must be set when DEBUG is disabled.")
+ALLOWED_HOSTS = _allowed_hosts.split(",")
 
 # It must be a full url: https://mydomain.com
 CSRF_TRUSTED_ORIGINS = os.environ.get("CSRF_TRUSTED_ORIGINS", "http://localhost").split(",")

gateway/tests/main/test_settings.py

@@ -19,6 +19,7 @@
 import importlib
 import os
 import sys
+from unittest.mock import patch
 
 import pytest
 from django.conf import settings
@@ -93,6 +94,39 @@ def test_debug_enabled_sets_debug_log_level(monkeypatch):
     assert main.settings.LOG_LEVEL == "DEBUG"
 
 
+def test_allowed_hosts_required_when_debug_off(monkeypatch):
+    """Unset ALLOWED_HOSTS with DEBUG off fails closed in production."""
+    monkeypatch.setenv("DEBUG", "0")
+    monkeypatch.delenv("ALLOWED_HOSTS", raising=False)
+
+    # Hide pytest from sys.modules only for this reload so IS_TEST is False
+    # and the production guard is actually exercised.
+    with patch.dict("sys.modules"):
+        sys.modules.pop("pytest", None)
+        with pytest.raises(ImproperlyConfigured):
+            importlib.reload(main.settings)
+
+
+def test_allowed_hosts_wildcard_when_debug_on(monkeypatch):
+    """Unset ALLOWED_HOSTS with DEBUG on defaults to the wildcard."""
+    monkeypatch.setenv("DEBUG", "1")
+    monkeypatch.delenv("ALLOWED_HOSTS", raising=False)
+
+    importlib.reload(main.settings)
+
+    assert main.settings.ALLOWED_HOSTS == ["*"]
+
+
+def test_allowed_hosts_uses_set_value(monkeypatch):
+    """A set ALLOWED_HOSTS value is used as-is, split on commas."""
+    monkeypatch.setenv("DEBUG", "0")
+    monkeypatch.setenv("ALLOWED_HOSTS", "example.com")
+
+    importlib.reload(main.settings)
+
+    assert main.settings.ALLOWED_HOSTS == ["example.com"]
+
+
 class TestAuthMechanism:
     """Tests for SETTINGS_AUTH_MECHANISM handling in main.settings."""
 

gateway/tox.ini

@@ -21,6 +21,9 @@ setenv =
   LANGUAGE=en_US
   LC_ALL=en_US.utf-8
   PROTOCOL_BUFFERS_PYTHON_IMPLEMENTATION=python
+  # Settings fail closed without ALLOWED_HOSTS when DEBUG is off; lint and import
+  # checks import the settings module, so give them a local value.
+  ALLOWED_HOSTS=localhost
   # Local-only dev secret so static analysis tools (pylint-django, import-linter)
   # can import Django settings, which now fail closed with DEBUG off and no key.
   DJANGO_SECRET_KEY=django-insecure-tox-only-change-me