set capacity to 0 if instance has not checked in lately

awx/main/models/ha.py

@@ -5,6 +5,8 @@ from django.db import models
 from django.db.models.signals import post_save
 from django.dispatch import receiver
 from django.utils.translation import ugettext_lazy as _
+from django.conf import settings
+from django.utils.timezone import now, timedelta
 
 from solo.models import SingletonModel
 
@@ -53,6 +55,14 @@ class Instance(models.Model):
         # NOTE: TODO: Likely to repurpose this once standalone ramparts are a thing
         return "awx"
 
+    def is_lost(self, ref_time=None, isolated=False):
+        if ref_time is None:
+            ref_time = now()
+        grace_period = 120
+        if isolated:
+            grace_period = settings.AWX_ISOLATED_PERIODIC_CHECK * 2
+        return self.modified < ref_time - timedelta(seconds=grace_period)
+
 
 class InstanceGroup(models.Model):
     """A model representing a Queue/Group of AWX Instances."""