Check model supports cron-style schedule

hc/api/migrations/0027_auto_20161205_0833.py

@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.10.1 on 2016-12-05 08:33
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('api', '0026_auto_20160415_1824'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='check',
+            name='schedule',
+            field=models.CharField(blank=True, max_length=100),
+        ),
+        migrations.AddField(
+            model_name='check',
+            name='tz',
+            field=models.CharField(default='UTC', max_length=36),
+        ),
+        migrations.AlterField(
+            model_name='channel',
+            name='kind',
+            field=models.CharField(choices=[('email', 'Email'), ('webhook', 'Webhook'), ('hipchat', 'HipChat'), ('slack', 'Slack'), ('pd', 'PagerDuty'), ('po', 'Pushover'), ('pushbullet', 'Pushbullet'), ('opsgenie', 'OpsGenie'), ('victorops', 'VictorOps')], max_length=20),
+        ),
+    ]

hc/api/models.py

@@ -3,8 +3,9 @@
 import hashlib
 import json
 import uuid
-from datetime import timedelta as td
+from datetime import datetime, timedelta as td
 
+from croniter import croniter
 from django.conf import settings
 from django.contrib.auth.models import User
 from django.db import models
@@ -53,6 +54,8 @@ class Check(models.Model):
     created = models.DateTimeField(auto_now_add=True)
     timeout = models.DurationField(default=DEFAULT_TIMEOUT)
     grace = models.DurationField(default=DEFAULT_GRACE)
+    schedule = models.CharField(max_length=100, blank=True)
+    tz = models.CharField(max_length=36, default="UTC")
     n_pings = models.IntegerField(default=0)
     last_ping = models.DateTimeField(null=True, blank=True)
     alert_after = models.DateTimeField(null=True, blank=True, editable=False)
@@ -85,27 +88,45 @@ class Check(models.Model):
 
         return errors
 
-    def get_status(self):
+    def get_grace_start(self):
+        """ Return the datetime when grace period starts. """
+
+        # The common case, grace starts after timeout
+        if not self.schedule:
+            return self.last_ping + self.timeout
+
+        # The complex case, next ping is expected based on cron schedule
+        with timezone.override(self.tz):
+            last_naive = timezone.make_naive(self.last_ping)
+            it = croniter(self.schedule, last_naive)
+            next_naive = it.get_next(datetime)
+            return timezone.make_aware(next_naive, is_dst=False)
+
+    def get_status(self, now=None):
+        """ Return "up" if the check is up or in grace, otherwise "down". """
+
         if self.status in ("new", "paused"):
             return self.status
 
-        now = timezone.now()
+        if now is None:
+            now = timezone.now()
 
-        if self.last_ping + self.timeout + self.grace > now:
-            return "up"
-
-        return "down"
+        return "up" if self.get_grace_start() + self.grace > now else "down"
 
     def get_alert_after(self):
-        return self.last_ping + self.timeout + self.grace
+        """ Return the datetime when check potentially goes down. """
+
+        return self.get_grace_start() + self.grace
 
     def in_grace_period(self):
+        """ Return True if check is currently in grace period. """
+
         if self.status in ("new", "paused"):
             return False
 
-        up_ends = self.last_ping + self.timeout
-        grace_ends = up_ends + self.grace
-        return up_ends < timezone.now() < grace_ends
+        grace_start = self.get_grace_start()
+        grace_end = grace_start + self.grace
+        return grace_start < timezone.now() < grace_end
 
     def assign_all_channels(self):
         if self.user:

hc/api/tests/test_check_model.py

@@ -1,4 +1,4 @@
-from datetime import timedelta
+from datetime import datetime, timedelta
 
 from django.test import TestCase
 from django.utils import timezone
@@ -37,3 +37,40 @@ class CheckModelTestCase(TestCase):
 
         check.status = "paused"
         self.assertFalse(check.in_grace_period())
+
+    def test_status_works_with_cron_syntax(self):
+        dt = timezone.make_aware(datetime(2000, 1, 1), timezone=timezone.utc)
+
+        # Expect ping every midnight, default grace is 1 hour
+        check = Check()
+        check.timeout = timedelta(minutes=0)
+        check.schedule = "0 0 * * *"
+        check.status = "up"
+        check.last_ping = dt
+
+        # 00:30am
+        now = dt + timedelta(days=1, minutes=30)
+        self.assertEqual(check.get_status(now), "up")
+
+        # 1:30am
+        now = dt + timedelta(days=1, minutes=90)
+        self.assertEqual(check.get_status(now), "down")
+
+    def test_status_works_with_timezone(self):
+        dt = timezone.make_aware(datetime(2000, 1, 1), timezone=timezone.utc)
+
+        # Expect ping every day at 10am, default grace is 1 hour
+        check = Check()
+        check.timeout = timedelta(minutes=0)
+        check.schedule = "0 10 * * *"
+        check.status = "up"
+        check.last_ping = dt
+        check.tz = "Australia/Brisbane"  # UTC+10
+
+        # 10:30am
+        now = dt + timedelta(days=1, minutes=30)
+        self.assertEqual(check.get_status(now), "up")
+
+        # 11:30am
+        now = dt + timedelta(days=1, minutes=90)
+        self.assertEqual(check.get_status(now), "down")

requirements.txt

@@ -1,3 +1,4 @@
+croniter
 django-appconf==1.0.1
 django-ses-backend==0.1.1
 Django==1.10.1
@@ -5,4 +6,5 @@ django_compressor==2.1
 djmail==0.11.0
 premailer==2.9.6
 psycopg2==2.6.1
+pytz==2016.7
 requests==2.9.1