Handle Tailscale Device Missing lastSeen field (#92)

* handle missing lastSeen

* make devicesnapshot migration

* fix pre-commit

* skips devices with no lastSeen while scanning for stale device

* add tests to handle devices with no lastSeen

* fix pre-commit

Author: HusnaHariz

apps/tailscale/migrations/0003_alter_devicesnapshot_last_seen.py

@@ -0,0 +1,19 @@
+# Generated by Django 5.2.2 on 2025-10-09 21:02
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("tailscale", "0002_devicesnapshot_device_alter_device_latest_snapshot"),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name="devicesnapshot",
+            name="last_seen",
+            field=models.DateTimeField(
+                blank=True, help_text="When device was last active on the tailnet.", null=True
+            ),
+        ),
+    ]

apps/tailscale/models.py

@@ -100,7 +100,9 @@ class DeviceSnapshot(models.Model):
         null=True, blank=True, help_text="The expiration date of the device's auth key."
     )
     hostname = models.CharField(max_length=255, help_text="The machine name in the admin console.")
-    last_seen = models.DateTimeField(help_text="When device was last active on the tailnet.")
+    last_seen = models.DateTimeField(
+        null=True, blank=True, help_text="When device was last active on the tailnet."
+    )
     name = models.CharField(max_length=255, help_text="The MagicDNS name of the device.")
     node_id = models.CharField(max_length=128, help_text="The preferred identifier for a device.")
     os = models.CharField(

dagster_publish_mdm/assets/tailscale/tailscale_devices.py

@@ -49,7 +49,7 @@ def tailscale_append_device_snapshot_table(
             created=device["created"],
             expires=expires,
             hostname=device["hostname"],
-            last_seen=device["lastSeen"],
+            last_seen=device.get("lastSeen"),
             name=device["name"],
             node_id=device["nodeId"],
             os=device["os"],
@@ -111,13 +111,16 @@ def stale_tailscale_devices(
         hostname = device.get("hostname")
         device_id = device.get("id")
 
-        try:
-            seen_time = dt.datetime.fromisoformat(last_seen.replace("Z", "+00:00"))
-            if seen_time < time_delta:
-                context.log.info(f"Device {hostname} last seen at {seen_time} — marking as stale.")
-                stale_devices.append(device)
-        except Exception as e:
-            context.log.warning(f"Failed to process device {hostname}: (ID: {device_id}) {e}")
+        if last_seen:
+            try:
+                seen_time = dt.datetime.fromisoformat(last_seen.replace("Z", "+00:00"))
+                if seen_time < time_delta:
+                    context.log.info(
+                        f"Device {hostname} last seen at {seen_time} — marking as stale."
+                    )
+                    stale_devices.append(device)
+            except Exception as e:
+                context.log.warning(f"Failed to process device {hostname}: (ID: {device_id}) {e}")
 
     context.add_output_metadata({"Stale Devices Preview": stale_devices[:2]})
     return stale_devices

tests/dagster_publish_mdm/tailscale/test_tailscale_devices.py

@@ -95,6 +95,17 @@ def test_device_no_expiration(devices):
     assert device.expires is None
 
 
+@pytest.mark.django_db
+def test_device_with_no_last_seen(devices):
+    """Test asset handles devices JSON with no last seen."""
+    devices["devices"][0].pop("lastSeen")
+    assets.tailscale_append_device_snapshot_table(
+        context=dg.build_asset_context(), tailscale_device_snapshot=devices
+    )
+    device = DeviceSnapshot.objects.first()
+    assert device.last_seen is None
+
+
 @pytest.mark.django_db
 def test_tailscale_insert_and_update_devices(devices):
     """Test asset inserts and updates devices."""
@@ -186,3 +197,31 @@ def test_stale_tailscale_devices(monkeypatch):
         dg.build_asset_context(), tailscale_device_snapshot=snapshot
     )
     assert len(result) == 1
+
+
+def test_stale_tailscale_devices_with_no_last_seen(monkeypatch):
+    """Test stale devices asset handles devices with no last seen."""
+
+    now = dt.datetime.now(dt.timezone.utc)
+    monkeypatch.delenv("TAILSCALE_DEVICE_STALE_MINUTES", raising=False)
+
+    # Only one device: device-3, should be marked stale.
+    snapshot = {
+        "devices": [
+            {
+                "id": "1",
+                "hostname": "device-1",
+            },  # Device with no last seen, meaning its connected. Should NOT be deleted.
+            {
+                "id": "2",
+                "hostname": "device-2",
+                "lastSeen": (now - dt.timedelta(days=90, seconds=1)).strftime(
+                    TAILSCALE_FORMAT
+                ),  # Device inactive for 90 days + 1 sec. Should be deleted.
+            },
+        ]
+    }
+    result = assets.stale_tailscale_devices(
+        dg.build_asset_context(), tailscale_device_snapshot=snapshot
+    )
+    assert len(result) == 1