Fix sendalerts crash loop when encountering a bad cron schedule

CHANGELOG.md

@@ -19,7 +19,7 @@ All notable changes to this project will be documented in this file.
 - Increase the allowable length of Matrix room alias to 100 (#320)
 - Make sure Check.last_ping and Ping.created timestamps match exactly
 - Don't trigger "down" notifications when changing schedule interactively in web UI
-
+- Fix sendalerts crash loop when encountering a bad cron schedule
 
 ## v1.12.0 - 2020-01-02
 

hc/api/management/commands/sendalerts.py

@@ -1,3 +1,4 @@
+from datetime import timedelta as td
 import time
 from threading import Thread
 
@@ -103,7 +104,16 @@ class Command(BaseCommand):
         old_status = check.status
         q = Check.objects.filter(id=check.id, status=old_status)
 
-        if check.get_status(with_started=False) != "down":
+        try:
+            status = check.get_status(with_started=False)
+        except Exception as e:
+            # Make sure we don't trip on this check again for an hour:
+            # Otherwise sendalerts may end up in a crash loop.
+            q.update(alert_after=now + td(hours=1))
+            # Then re-raise the exception:
+            raise e
+
+        if status != "down":
             # It is not down yet. Update alert_after
             q.update(alert_after=check.going_down_after())
             return True