Check.in_grace_period() looks at `last_ping_was_fail` flag.

hc/api/models.py

@@ -146,6 +146,9 @@ class Check(models.Model):
         if self.status in ("new", "paused"):
             return False
 
+        if self.last_ping_was_fail:
+            return False
+
         grace_start = self.get_grace_start()
         grace_end = grace_start + self.grace
         return grace_start < timezone.now() < grace_end

hc/api/tests/test_check_model.py

@@ -20,6 +20,16 @@ class CheckModelTestCase(TestCase):
         check = Check()
         self.assertFalse(check.in_grace_period())
 
+    def test_in_grace_period_handles_fail_ping(self):
+        check = Check()
+        check.status = "up"
+        check.last_ping = timezone.now() - timedelta(days=1, minutes=30)
+        check.last_ping_was_fail = True
+
+        # If last ping was signalling a failure, we're not in grace period,
+        # we're down
+        self.assertFalse(check.in_grace_period())
+
     def test_status_works_with_grace_period(self):
         check = Check()
         check.status = "up"