Add errorhandling for missing cache in ranked statistics

python/nav/web/sortedstats/views.py

@@ -26,14 +26,27 @@
 from django.shortcuts import render
 from django.core.cache import caches
 from django.conf import settings
+from django.core.cache.backends.base import InvalidCacheBackendError
 
 from .forms import ViewForm
 from . import CLASSMAP, TIMEFRAMES
 from nav.metrics.errors import GraphiteUnreachableError
 
 GRAPHITE_TIME_FORMAT = "%H:%M_%Y%m%d"
 _logger = logging.getLogger(__name__)
-cache = caches['sortedstats']
+
+
+def get_cache():
+    return caches['sortedstats']
+
+
+def cache_is_misconfigured():
+    try:
+        get_cache()
+    except InvalidCacheBackendError:
+        return True
+    else:
+        return False
 
 
 def index(request):
@@ -64,6 +77,7 @@ def index(request):
         'graphite_unreachable': graphite_unreachable,
         'from_cache': from_cache,
         'duration': duration,
+        'cache_misconfigured': cache_is_misconfigured(),
     }
 
     return render(request, 'sortedstats/sortedstats.html', context)
@@ -78,8 +92,13 @@ def process_form(form):
     rows = form.cleaned_data['rows']
     cache_key = get_cache_key(view, timeframe, rows)
     if form.cleaned_data['use_cache']:
-        result = cache.get(cache_key)
-        if result and not result.data:
+        try:
+            cache = get_cache()
+            result = cache.get(cache_key)
+            if result and not result.data:
+                result = None
+        except InvalidCacheBackendError as e:
+            _logger.error("Error accessing cache for ranked statistics: %s", e)
             result = None
     if not result:
         result = collect_result(view, timeframe, rows)
@@ -106,7 +125,11 @@ def collect_result(view, timeframe, rows):
     cache_key = get_cache_key(view, timeframe, rows)
     result = get_result(view, start, end, rows)
     result.collect()
-    cache.set(cache_key, result, timeout=timeout)
+    try:
+        cache = get_cache()
+        cache.set(cache_key, result, timeout=timeout)
+    except InvalidCacheBackendError as e:
+        _logger.error("Error accessing cache for ranked statistics: %s", e)
     return result
 
 

python/nav/web/templates/sortedstats/sortedstats.html

@@ -17,6 +17,11 @@
     {% include 'nav_header.html' %}
   {% endwith %}
 
+  {% if cache_misconfigured %}
+    <div class="alert-box error">
+      The cache for Ranked Statistics is not configured correctly.
+    </div>
+  {% endif %}
 
   {% crispy form %}
 

tests/unittests/web/sortedstats/sortedstats_test.py

@@ -26,10 +26,10 @@ def test_cache_key_is_correct(self):
         cache_key = views.get_cache_key(view, timeframe, rows)
         self.assertEqual(cache_key, expected_cache_key)
 
-    @patch('nav.web.sortedstats.views.cache')
+    @patch('nav.web.sortedstats.views.get_cache')
     def test_process_form_returns_cache_value_if_cache_exists(self, cache_mock):
         data = "cached"
-        cache_mock.get.return_value.data = data
+        cache_mock.return_value.get.return_value.data = data
         fake_form = MagicMock()
         fake_form.cleaned_data = {
             'view': 'uptime',
@@ -42,12 +42,12 @@ def test_process_form_returns_cache_value_if_cache_exists(self, cache_mock):
         self.assertEqual(result.data, data)
 
     @patch('nav.web.sortedstats.views.collect_result')
-    @patch('nav.web.sortedstats.views.cache')
+    @patch('nav.web.sortedstats.views.get_cache')
     def test_cache_not_used_if_empty_and_use_cache_is_on(
         self, cache_mock, collect_mock
     ):
         data = "new"
-        cache_mock.get.return_value.data = ""
+        cache_mock.return_value.get.return_value.data = ""
         collect_mock.return_value.data = data
         fake_form = MagicMock()
         fake_form.cleaned_data = {
@@ -61,12 +61,12 @@ def test_cache_not_used_if_empty_and_use_cache_is_on(
         self.assertEqual(result.data, data)
 
     @patch('nav.web.sortedstats.views.collect_result')
-    @patch('nav.web.sortedstats.views.cache')
+    @patch('nav.web.sortedstats.views.get_cache')
     def test_cache_not_used_if_empty_and_use_cache_is_off(
         self, cache_mock, collect_mock
     ):
         data = "new"
-        cache_mock.get.return_value.data = ""
+        cache_mock.return_value.get.return_value.data = ""
         collect_mock.return_value.data = data
         fake_form = MagicMock()
         fake_form.cleaned_data = {