Insert middleware to intercept Datahub connection exceptions

core/middleware.py

@@ -0,0 +1,19 @@
+import logging
+
+from data_platform_catalogue.client.exceptions import ConnectivityError
+from django.shortcuts import render
+
+logger = logging.getLogger(__name__)
+
+
+class CustomErrorMiddleware:
+    def __init__(self, get_response):
+        self.get_response = get_response
+
+    def __call__(self, request):
+        return self.get_response(request)
+
+    def process_exception(self, request, exception):
+        if isinstance(exception, ConnectivityError):
+            logger.exception(exception)
+            return render(request, "500_datahub_unavailable.html", status=500)

core/settings.py

@@ -53,6 +53,7 @@
     "django.contrib.auth.middleware.AuthenticationMiddleware",
     "django.contrib.messages.middleware.MessageMiddleware",
     "django.middleware.clickjacking.XFrameOptionsMiddleware",
+    "core.middleware.CustomErrorMiddleware",
     "django_prometheus.middleware.PrometheusAfterMiddleware",
 ]
 

core/urls.py

@@ -17,7 +17,6 @@
 
 from django.contrib import admin
 from django.urls import include, path
-from django.views.generic import TemplateView
 
 
 def trigger_error(request):
@@ -29,8 +28,4 @@ def trigger_error(request):
     path("sentry-debug/", trigger_error),
     path("", include("home.urls", namespace="home")),
     path("", include("django_prometheus.urls")),
-    path(
-        "unavailable",
-        TemplateView.as_view(template_name="500_datahub_unavailable.html"),
-    ),
 ]

lib/datahub-client/data_platform_catalogue/client/datahub_client.py

@@ -5,7 +5,7 @@
 
 from data_platform_catalogue.client.exceptions import (
     AspectDoesNotExist,
-    CatalogueError,
+    ConnectivityError,
     EntityDoesNotExist,
     InvalidDomain,
     ReferencedEntityMissing,
@@ -38,6 +38,7 @@
     SearchResponse,
     SortOption,
 )
+from datahub.configuration.common import ConfigurationError
 from datahub.emitter import mce_builder
 from datahub.emitter.mcp import MetadataChangeProposalWrapper
 from datahub.ingestion.graph.client import DatahubClientConfig, DataHubGraph
@@ -110,12 +111,17 @@ def __init__(self, jwt_token, api_url: str, graph=None):
         elif api_url.endswith("/api"):
             self.gms_endpoint = api_url + "/gms"
         else:
-            raise CatalogueError("api_url is incorrectly formatted")
+            raise ConnectivityError("api_url is incorrectly formatted")
 
         self.server_config = DatahubClientConfig(
             server=self.gms_endpoint, token=jwt_token
         )
-        self.graph = graph or DataHubGraph(self.server_config)
+
+        try:
+            self.graph = graph or DataHubGraph(self.server_config)
+        except ConfigurationError as e:
+            raise ConnectivityError from e
+
         self.search_client = SearchClient(self.graph)
 
         self.dataset_query = (

lib/datahub-client/data_platform_catalogue/client/exceptions.py

@@ -4,6 +4,12 @@ class CatalogueError(Exception):
     """
 
 
+class ConnectivityError(CatalogueError):
+    """
+    Unable to collect to the Datahub catalog
+    """
+
+
 class ReferencedEntityMissing(CatalogueError):
     """
     A referenced entity (such as a user or tag) does not yet exist when

tests/core/test_middleware.py

@@ -0,0 +1,27 @@
+from unittest.mock import MagicMock
+
+from data_platform_catalogue.client.exceptions import ConnectivityError
+
+from core.middleware import CustomErrorMiddleware
+
+
+def test_middleware_renders_connectivity_response():
+    get_response = MagicMock()
+    request = MagicMock()
+    middleware = CustomErrorMiddleware(get_response)
+    error = ConnectivityError()
+    response = middleware.process_exception(request, error)
+
+    assert response
+    assert b"Catalogue service unavailable" in response.content
+    assert response.status_code == 500
+
+
+def test_middleware_ignores_other_errors():
+    get_response = MagicMock()
+    request = MagicMock()
+    middleware = CustomErrorMiddleware(get_response)
+    error = Exception()
+    response = middleware.process_exception(request, error)
+
+    assert response is None