feat: health check

codeforlife/settings/custom.py

@@ -40,3 +40,7 @@
 
 # The name of the session metadata cookie.
 SESSION_METADATA_COOKIE_NAME = "session_metadata"
+
+# App deployment details.
+APP_ID = os.getenv("APP_ID", "REPLACE_ME")
+APP_VERSION = os.getenv("APP_VERSION", "REPLACE_ME")

codeforlife/urls/patterns.py

@@ -11,7 +11,7 @@
 from rest_framework import status
 
 from ..settings import SERVICE_IS_ROOT, SERVICE_NAME
-from ..views import CsrfCookieView, LogoutView
+from ..views import CsrfCookieView, HealthCheckView, LogoutView
 
 UrlPatterns = t.List[t.Union[URLResolver, URLPattern]]
 
@@ -36,6 +36,11 @@ def get_urlpatterns(
             admin.site.urls,
             name="admin",
         ),
+        path(
+            "health-check/",
+            HealthCheckView.as_view(),
+            name="health-check",
+        ),
         path(
             "api/csrf/cookie/",
             CsrfCookieView.as_view(),

codeforlife/views/__init__.py

@@ -7,4 +7,5 @@
 from .base_login import BaseLoginView
 from .common import CsrfCookieView, LogoutView
 from .decorators import action, cron_job
+from .health_check import HealthCheckView
 from .model import BaseModelViewSet, ModelViewSet

codeforlife/views/health_check.py

@@ -0,0 +1,126 @@
+"""
+© Ocado Group
+Created on 14/11/2024 at 16:31:56(+00:00).
+"""
+
+import typing as t
+from dataclasses import dataclass
+from datetime import datetime
+
+from django.apps import apps
+from django.conf import settings
+from django.contrib.sites.models import Site
+from django.views.decorators.cache import cache_page
+from rest_framework import status
+from rest_framework.request import Request
+from rest_framework.response import Response
+from rest_framework.views import APIView
+
+from ..permissions import AllowAny
+
+HealthStatus = t.Literal[
+    "healthy",
+    "startingUp",
+    "shuttingDown",
+    "unhealthy",
+    "unknown",
+]
+
+
+@dataclass(frozen=True)
+class HealthCheck:
+    """The health of the current service."""
+
+    @dataclass(frozen=True)
+    class Detail:
+        """A health detail."""
+
+        name: str
+        description: str
+        health: HealthStatus
+
+    health_status: HealthStatus
+    additional_info: str
+    details: t.Optional[t.List[Detail]] = None
+
+
+class HealthCheckView(APIView):
+    """A view for load balancers to determine whether the app is healthy."""
+
+    http_method_names = ["get"]
+    permission_classes = [AllowAny]
+    startup_timestamp = datetime.now().isoformat()
+    cache_timeout: float = 30
+
+    def get_health_check(self, request: Request) -> HealthCheck:
+        """Check the health of the current service."""
+        try:
+            if not apps.ready or not apps.apps_ready or not apps.models_ready:
+                return HealthCheck(
+                    health_status="startingUp",
+                    additional_info="Apps not ready.",
+                )
+
+            host = request.get_host()
+            if not Site.objects.filter(domain=host).exists():
+                return HealthCheck(
+                    health_status="unhealthy",
+                    additional_info=f'Site "{host}" does not exist.',
+                )
+
+            return HealthCheck(
+                health_status="healthy",
+                additional_info="All healthy.",
+            )
+        # pylint: disable-next=broad-exception-caught
+        except Exception as ex:
+            return HealthCheck(
+                health_status="unknown",
+                additional_info=str(ex),
+            )
+
+    def get(self, request: Request):
+        """Return a health check for the current service."""
+        health_check = self.get_health_check(request)
+
+        return Response(
+            data={
+                "appId": settings.APP_ID,
+                "healthStatus": health_check.health_status,
+                "lastCheckedTimestamp": datetime.now().isoformat(),
+                "additionalInformation": health_check.additional_info,
+                "startupTimestamp": self.startup_timestamp,
+                "appVersion": settings.APP_VERSION,
+                "details": [
+                    {
+                        "name": detail.name,
+                        "description": detail.description,
+                        "health": detail.health,
+                    }
+                    for detail in (health_check.details or [])
+                ],
+            },
+            status={
+                # The app is running normally.
+                "healthy": status.HTTP_200_OK,
+                # The app is performing app-specific initialisation which must
+                # complete before it will serve normal application requests
+                # (perhaps the app is warming a cache or something similar). You
+                # only need to use this status if your app will be in a start-up
+                # mode for a prolonged period of time.
+                "startingUp": status.HTTP_503_SERVICE_UNAVAILABLE,
+                # The app is shutting down. As with startingUp, you only need to
+                # use this status if your app takes a prolonged amount of time
+                # to shutdown, perhaps because it waits for a long-running
+                # process to complete before shutting down.
+                "shuttingDown": status.HTTP_503_SERVICE_UNAVAILABLE,
+                # The app is not running normally.
+                "unhealthy": status.HTTP_503_SERVICE_UNAVAILABLE,
+                # The app is not able to report its own state.
+                "unknown": status.HTTP_503_SERVICE_UNAVAILABLE,
+            }[health_check.health_status],
+        )
+
+    @classmethod
+    def as_view(cls, **initkwargs):
+        return cache_page(cls.cache_timeout)(super().as_view(**initkwargs))