lxd: do not restart instances via stop+start

paride · paride · commit ec561f00c144 · 2022-06-16T12:43:55.000+02:00
Ephemeral instanced do not survive being stopped, while they do survive
being restarted.
diff --git a/pycloudlib/instance.py b/pycloudlib/instance.py
@@ -89,7 +89,7 @@ def restart(self, wait=True, **kwargs):
         self._sync_filesystem()
         # If we're not waiting, just call subclass's restart and return.
         if not wait:
-            self._do_restart()
+            self._do_restart(**kwargs)
             return
 
         pre_boot_id = None
diff --git a/pycloudlib/lxd/instance.py b/pycloudlib/lxd/instance.py
@@ -315,15 +315,18 @@ def push_file(self, local_path, remote_path):
     def _do_restart(self, force=False, **kwargs):
         """Restart an instance.
 
-        For LXD this means stopping the instance, and then starting it.
-
         Args:
             force: boolean, force instance to shutdown before restart
         """
         self._log.debug("restarting %s", self.name)
 
-        self.shutdown(wait=True, force=force)
-        self.start(wait=False)
+        # Note: even if slightly faster in some cases, do not replace
+        # `lxc restart` with stop + start, as ephemeral instances do
+        # not survive being stopped, while they do survive restarts.
+        cmd = ["lxc", "restart", self.name]
+        if force:
+            cmd.append("--force")
+        subp(cmd)
 
     def restore(self, snapshot_name):
         """Restore instance from a specific snapshot.
diff --git a/pycloudlib/lxd/tests/test_instance.py b/pycloudlib/lxd/tests/test_instance.py
@@ -12,18 +12,23 @@ class TestRestart:
     """Tests covering pycloudlib.lxd.instance.Instance.restart."""
 
     @pytest.mark.parametrize("force", (False, True))
-    @mock.patch("pycloudlib.lxd.instance.LXDInstance.start")
-    @mock.patch("pycloudlib.lxd.instance.LXDInstance.shutdown")
-    @mock.patch("pycloudlib.lxd.instance.LXDInstance.wait")
     @mock.patch("pycloudlib.lxd.instance.subp")
-    def test_restart_calls_lxc_cmd_with_force_param(
-        self, _m_subp, _m_wait, m_shutdown, m_start, force
-    ):
-        """Honor force param on shutdown."""
+    def test_restart_calls_lxc_cmd_with_force_param(self, m_subp, force):
+        """Honor force param on restart."""
         instance = LXDInstance(name="my_vm")
         instance._do_restart(force=force)  # pylint: disable=protected-access
-        assert [mock.call(wait=True, force=force)] == m_shutdown.call_args_list
-        assert [mock.call(wait=False)] == m_start.call_args_list
+        if force:
+            assert "--force" in m_subp.call_args[0][0]
+        else:
+            assert "--force" not in m_subp.call_args[0][0]
+
+    @mock.patch("pycloudlib.lxd.instance.LXDInstance.shutdown")
+    @mock.patch("pycloudlib.lxd.instance.subp")
+    def test_restart_does_not_shutdown(self, _m_subp, m_shutdown):
+        """Don't shutdown (stop) instance on restart."""
+        instance = LXDInstance(name="my_vm")
+        instance._do_restart()  # pylint: disable=protected-access
+        assert not m_shutdown.called
 
 
 class TestExecute:
