Fix issue with settings being accessed at import time

Author: matthewelwell

src/common/core/main.py

@@ -9,7 +9,7 @@
 )
 
 from common.core.cli import healthcheck
-from common.prometheus.utils import prepare_prom_multiproc_dir
+from common.prometheus.multiprocessing import prepare_prom_multiproc_dir
 
 logger = logging.getLogger(__name__)
 

src/common/prometheus/__init__.py

@@ -1,3 +1,15 @@
-from common.prometheus.utils import Histogram
+from typing import Any
 
-__all__ = ("Histogram",)
+_utils = ("Histogram",)
+
+
+def __getattr__(name: str) -> Any:
+    """
+    Since utils imports settings, we lazy load any objects that we want to import to
+    prevent Django's settings-at-import-time trap
+    """
+    if name in _utils:
+        from common.prometheus import utils
+
+        return getattr(utils, name)
+    raise AttributeError(name)

src/common/prometheus/multiprocessing.py

@@ -0,0 +1,33 @@
+import os
+import pathlib
+import shutil
+from tempfile import gettempdir
+
+from common.core.constants import DEFAULT_PROMETHEUS_MULTIPROC_DIR_NAME
+
+
+def prepare_prom_multiproc_dir() -> None:
+    prom_dir = pathlib.Path(
+        os.environ.setdefault(
+            "PROMETHEUS_MULTIPROC_DIR",
+            os.path.join(gettempdir(), DEFAULT_PROMETHEUS_MULTIPROC_DIR_NAME),
+        )
+    )
+
+    if prom_dir.exists():
+        for p in prom_dir.rglob("*"):
+            try:
+                # Ensure that the cleanup doesn't silently fail on
+                # files and subdirs created by other users.
+                p.chmod(0o777)
+            except Exception:  # pragma: no cover
+                pass
+
+        shutil.rmtree(prom_dir, ignore_errors=True)
+
+    prom_dir.mkdir(parents=True, exist_ok=True)
+
+    # While `mkdir` sets mode=0o777 by default, this can be affected by umask resulting in
+    # lesser permissions for other users. This step ensures the directory is writable for
+    # all users.
+    prom_dir.chmod(0o777)

src/common/prometheus/utils.py

@@ -1,16 +1,10 @@
 import importlib
-import os
-import pathlib
-import shutil
-from tempfile import gettempdir
 
 import prometheus_client
 from django.conf import settings
 from prometheus_client.metrics import MetricWrapperBase
 from prometheus_client.multiprocess import MultiProcessCollector
 
-from common.core.constants import DEFAULT_PROMETHEUS_MULTIPROC_DIR_NAME
-
 
 class Histogram(prometheus_client.Histogram):
     DEFAULT_BUCKETS = settings.PROMETHEUS_HISTOGRAM_BUCKETS
@@ -42,30 +36,3 @@ def reload_metrics(*metric_module_names: str) -> None:
                 registry.unregister(module_attr)
 
         importlib.reload(metrics_module)
-
-
-def prepare_prom_multiproc_dir() -> None:
-    prom_dir = pathlib.Path(
-        os.environ.setdefault(
-            "PROMETHEUS_MULTIPROC_DIR",
-            os.path.join(gettempdir(), DEFAULT_PROMETHEUS_MULTIPROC_DIR_NAME),
-        )
-    )
-
-    if prom_dir.exists():
-        for p in prom_dir.rglob("*"):
-            try:
-                # Ensure that the cleanup doesn't silently fail on
-                # files and subdirs created by other users.
-                p.chmod(0o777)
-            except Exception:  # pragma: no cover
-                pass
-
-        shutil.rmtree(prom_dir, ignore_errors=True)
-
-    prom_dir.mkdir(parents=True, exist_ok=True)
-
-    # While `mkdir` sets mode=0o777 by default, this can be affected by umask resulting in
-    # lesser permissions for other users. This step ensures the directory is writable for
-    # all users.
-    prom_dir.chmod(0o777)