feat(instances): auto converge is on by default for a live migration

A VM that changes its memory faster than the network carries it does
not finish a live migration without auto converge (measured: a guest
rewriting about 1.2 GB/s did not finish in 90 s over an 8.5 Gbit/s
link, and finished in 16-18 s with it). Auto converge only slows the
VM's CPUs while the migration cannot keep up, so a calm VM is not
affected.

The migrate form ticks it for a running VM. The API already documented
it as on by default but read a left-out option as off; the serializer
now has the defaults (auto converge on, compress and unsafe off) for
JSON and form-encoded requests, and the schema shows them.

instances/api/serializers.py

@@ -91,6 +91,10 @@ class CreateInstanceSerializer(serializers.ModelSerializer):
 class MigrateSerializer(serializers.ModelSerializer):
     instance = Instance.objects.all().prefetch_related("userinstance_set")
     live = serializers.BooleanField(initial=True)
+    # left out, also from a form-encoded request: auto converge on
+    autoconverge = serializers.BooleanField(default=True)
+    compress = serializers.BooleanField(default=False)
+    unsafe = serializers.BooleanField(default=False)
 
     class Meta:
         model = MigrateInstance

instances/templates/instances/settings_tab.html

@@ -626,7 +626,7 @@
                 <div class="row">
                     <div class="col-sm-6 offset-3">
                         <div class="form-check form-switch">
-                            <input class="form-check-input" type="checkbox" name="autoconverge" value="true" id="autoconverge" {% if instance.status != 1 %}disabled{% endif %}>
+                            <input class="form-check-input" type="checkbox" name="autoconverge" value="true" id="autoconverge" {% if instance.status != 1 %}disabled{% else %}checked{% endif %}>
                             <label class="form-check-label" for="autoconverge" title="{% trans 'Forces CPU convergence during live migration' %}">{% trans "Auto converge" %}</label>
                         </div>
                     </div>

instances/test_migrate_form.py

@@ -0,0 +1,64 @@
+"""The migrate form ticks auto converge for a running VM, and the API uses
+the same default: it only slows a VM that the migration cannot keep up with."""
+
+import re
+from unittest.mock import patch
+
+import libvirt
+from computes.models import Compute
+from django.contrib.auth import get_user_model
+from django.test import TestCase
+from django.urls import reverse
+from instances.models import Instance
+from rest_framework.test import APIClient
+
+DOMAIN = """<domain type='test'><name>migrate-form-vm</name><memory unit='MiB'>128</memory><vcpu>1</vcpu>
+<os><type arch='i686'>hvm</type></os></domain>"""
+
+
+class MigrateFormTests(TestCase):
+    def setUp(self):
+        self.conn = libvirt.open("test:///default")
+        self.addCleanup(self.conn.close)
+        self.domain = self.conn.defineXML(DOMAIN)
+        self.addCleanup(self.remove_domain)
+        self.compute = Compute.objects.create(name="mf", hostname="localhost", login="", password="", type=4)
+        self.other = Compute.objects.create(name="mf-other", hostname="198.51.100.30", login="", password="", type=4)
+        self.vm = Instance.objects.create(compute=self.compute, name=self.domain.name(), uuid=self.domain.UUIDString())
+        for target, value in (("get_machine_types", ["pc"]), ("get_nwfilters", [])):
+            patcher = patch(f"vrtManager.connection.wvmConnect.{target}", return_value=value)
+            patcher.start()
+            self.addCleanup(patcher.stop)
+        self.admin = get_user_model().objects.create_superuser("mf-admin", "mf@example.com", "pw")
+
+    def remove_domain(self):
+        if self.domain.isActive():
+            self.domain.destroy()
+        self.domain.undefine()
+
+    def autoconverge_input(self):
+        self.client.force_login(self.admin)
+        with patch("vrtManager.connection.connection_manager.get_connection", return_value=self.conn):
+            page = self.client.get(reverse("instances:instance", args=[self.vm.id])).content.decode()
+        return re.search(r'<input[^>]*id="autoconverge"[^>]*>', page).group(0)
+
+    def test_auto_converge_is_ticked_for_a_running_vm(self):
+        self.domain.create()
+        self.assertIn("checked", self.autoconverge_input())
+
+    def test_a_shut_off_vm_has_no_auto_converge(self):
+        field = self.autoconverge_input()
+        self.assertIn("disabled", field)
+        self.assertNotIn("checked", field)
+
+    def test_the_api_uses_auto_converge_unless_told_otherwise(self):
+        api = APIClient()
+        api.force_authenticate(self.admin)
+        request = {"instance": self.vm.id, "target_compute": self.other.id, "live": True, "offline": False}
+        with patch("instances.api.viewsets.migrate_instance", return_value="live") as migrate:
+            for encoding in ("json", "multipart"):
+                api.post("/api/v1/migrate/", request, format=encoding)
+            api.post("/api/v1/migrate/", {**request, "autoconverge": False}, format="json")
+            api.post("/api/v1/migrate/", {**request, "unsafe": True}, format="json")
+        self.assertEqual([c.kwargs["autoconverge"] for c in migrate.call_args_list], [True, True, False, True])
+        self.assertEqual([c.kwargs["unsafe"] for c in migrate.call_args_list], [False, False, False, True])