feat(admin): list and remove the owners kept for vanished VMs

A VM that disappears from its compute keeps its owners in a tombstone
until INSTANCE_OWNERSHIP_RETENTION_DAYS pass, but nothing showed them.
Superusers now see them on the "Removed VMs" admin page (name, UUID,
owners, removed, expires) and can remove one, so a VM deleted on
purpose no longer hands its owners to a later VM with the same UUID.

admin/templates/admin/tombstone_list.html

@@ -0,0 +1,63 @@
+{% extends "base.html" %}
+{% load i18n %}
+{% load static %}
+{% load bootstrap_icons %}
+{% block title %}{% trans "Removed VMs" %}{% endblock %}
+{% block content %}
+<div class="row">
+    <div class="col-lg-12">
+        {% include 'search_block.html' %}
+        <h1 class="page-header">{% trans "Removed VMs" %}</h1>
+        <p class="text-muted">{% trans "VMs that vanished from their compute. Their owners come back if the same UUID shows up again before the record expires." %}</p>
+    </div>
+</div>
+<div class="row">
+    {% if not tombstones %}
+        <div class="col-lg-12">
+            <div class="alert alert-info shadow-sm">
+                {% bs_icon 'info-circle' %} {% trans "No removed VMs" %}
+            </div>
+        </div>
+    {% else %}
+        <div class="col-lg-12">
+            <table class="table table-striped table-hover">
+                <thead>
+                    <tr>
+                        <th span="col">{% trans "Name" %}</th>
+                        <th span="col">{% trans "UUID" %}</th>
+                        <th span="col">{% trans "Owners" %}</th>
+                        <th span="col">{% trans "Removed" %}</th>
+                        <th span="col">{% trans "Expires" %}</th>
+                        <th span="col">{% trans "Actions" %}</th>
+                    </tr>
+                </thead>
+                <tbody class="searchable">
+                {% for tombstone in tombstones %}
+                    <tr>
+                        <td>
+                            <strong>{{ tombstone.name }}</strong>
+                            {% if tombstone.is_template %}<span class="badge bg-secondary">{% trans "Template" %}</span>{% endif %}
+                        </td>
+                        <td>{{ tombstone.uuid }}</td>
+                        <td>{{ tombstone.owner_names|join:", " }}</td>
+                        <td>{{ tombstone.removed|date:"Y-m-d H:i" }}</td>
+                        <td>{{ tombstone.expires|date:"Y-m-d H:i" }}</td>
+                        <td>
+                            <div class="float-end btn-group">
+                                <a class="btn btn-danger" href="{% url 'admin:tombstone_delete' tombstone.id %}" title="{% trans "Delete" %}">
+                                    {% bs_icon 'x' %}
+                                </a>
+                            </div>
+                        </td>
+                    </tr>
+                {% endfor %}
+                </tbody>
+            </table>
+        </div>
+    {% endif %}
+</div>
+{% endblock content %}
+
+{% block script %}
+<script src="{% static 'js/filter-table.js' %}"></script>
+{% endblock script %}

admin/test_tombstones.py

@@ -0,0 +1,56 @@
+"""Superusers list the ownership kept for VMs that vanished and can remove it."""
+
+from datetime import timedelta
+
+from django.contrib.auth.models import User
+from django.test import TestCase, override_settings
+from django.urls import reverse
+from django.utils import timezone
+
+from instances.models import InstanceTombstone
+
+UUID = "00000000-0000-4000-8000-000000000001"
+
+
+class TombstoneTests(TestCase):
+    def setUp(self):
+        self.client.force_login(User.objects.create_superuser("ts-admin", "ts@example.com", "pw"))
+        self.owner = User.objects.create_user("ts-owner", password="pw")
+        self.tombstone = InstanceTombstone.objects.create(
+            uuid=UUID,
+            name="ts-vm",
+            owners=[
+                {"user": self.owner.id, "is_change": True, "is_delete": False, "is_vnc": True},
+                {"user": 999999, "is_change": False, "is_delete": False, "is_vnc": False},
+            ],
+        )
+
+    @override_settings(INSTANCE_OWNERSHIP_RETENTION_DAYS=7)
+    def test_the_list_shows_the_vm_its_owners_and_when_it_expires(self):
+        removed = timezone.now() - timedelta(days=2)
+        InstanceTombstone.objects.filter(pk=self.tombstone.pk).update(removed=removed)
+        response = self.client.get(reverse("admin:tombstone_list"))
+        self.assertEqual(response.status_code, 200)
+        row = response.context["tombstones"][0]
+        self.assertEqual(row.owner_names, ["ts-owner", "deleted user"])
+        self.assertEqual(row.expires, removed + timedelta(days=7))
+        self.assertContains(response, "ts-vm")
+        self.assertContains(response, UUID)
+        self.assertContains(response, "ts-owner")
+
+    def test_only_superusers_see_or_remove_them(self):
+        self.client.force_login(self.owner)
+        self.assertEqual(self.client.get(reverse("admin:tombstone_list")).status_code, 403)
+        url = reverse("admin:tombstone_delete", args=[self.tombstone.pk])
+        self.assertEqual(self.client.post(url).status_code, 403)
+        self.assertTrue(InstanceTombstone.objects.exists())
+
+    def test_a_get_only_asks_for_confirmation(self):
+        response = self.client.get(reverse("admin:tombstone_delete", args=[self.tombstone.pk]))
+        self.assertContains(response, "ts-vm")
+        self.assertTrue(InstanceTombstone.objects.exists())
+
+    def test_a_post_removes_it(self):
+        response = self.client.post(reverse("admin:tombstone_delete", args=[self.tombstone.pk]))
+        self.assertRedirects(response, reverse("admin:tombstone_list"))
+        self.assertFalse(InstanceTombstone.objects.exists())

admin/urls.py

@@ -15,4 +15,6 @@ urlpatterns = [
     path("users/<int:pk>/block/", views.user_block, name="user_block"),
     path("users/<int:pk>/unblock/", views.user_unblock, name="user_unblock"),
     path("logs/", views.logs, name="logs"),
+    path("removed-vms/", views.tombstone_list, name="tombstone_list"),
+    path("removed-vms/<int:pk>/delete/", views.tombstone_delete, name="tombstone_delete"),
 ]

admin/views.py

@@ -1,3 +1,5 @@
+from datetime import timedelta
+
 from accounts.models import Instance, UserAttributes, UserInstance
 from appsettings.settings import app_settings
 from django.conf import settings
@@ -10,6 +12,7 @@ from django.shortcuts import get_object_or_404, redirect, render
 from django.utils.http import url_has_allowed_host_and_scheme
 from django.utils.translation import gettext_lazy as _
 from django.views.decorators.http import require_POST
+from instances.models import InstanceTombstone
 from logs.models import Logs
 
 from . import forms
@@ -210,6 +213,34 @@ def logs(request):
     return render(request, "admin/logs.html", {"logs": logs})
 
 
+@superuser_only
+def tombstone_list(request):
+    """The owners kept for VMs that vanished from their compute, in case the
+    same UUID comes back."""
+    tombstones = list(InstanceTombstone.objects.order_by("-removed"))
+    ids = {owner["user"] for tombstone in tombstones for owner in tombstone.owners}
+    names = dict(User.objects.filter(id__in=ids).values_list("id", "username"))
+    retention = timedelta(days=getattr(settings, "INSTANCE_OWNERSHIP_RETENTION_DAYS", 30))
+    for tombstone in tombstones:
+        tombstone.owner_names = [names.get(owner["user"], _("deleted user")) for owner in tombstone.owners]
+        tombstone.expires = tombstone.removed + retention
+    return render(request, "admin/tombstone_list.html", {"tombstones": tombstones})
+
+
+@superuser_only
+def tombstone_delete(request, pk):
+    tombstone = get_object_or_404(InstanceTombstone, pk=pk)
+    if request.method == "POST":
+        tombstone.delete()
+        return redirect("admin:tombstone_list")
+
+    return render(
+        request,
+        "common/confirm_delete.html",
+        {"object": tombstone},
+    )
+
+
 def add_default_instances(user):
     """
     Adds instances listed in NEW_USER_DEFAULT_INSTANCES to user