Add upgrade check about old computes

Report a warning during upgrade checks if there are computes older than
the previous major nova release in the system.

So if code is upgraded to N+1 and the upgrade check was run before
the restart of the services with N+1 code then the check warns for N-1
computes in the system.

Conflicts:
  doc/source/cli/nova-status.rst
  doc/source/install/verify.rst
  nova/cmd/status.py
  nova/tests/unit/cmd/test_status.py

Note: Fixed trivial conflicts due to different amount of upgrade
checks exists on ussuri than on victoria (the patch that is missing
from Ussuri is Ic4d3b998bb9701cb1e3ef12d9bb6f4d91cc19c18). Also needed
to use six.text_type() instead of str() due to used hacking package
(and thus flake8) requires it still on Ussuri.

Related-Bug: #1903545

Change-Id: I873b0c1e6e695ae88241bbf75ac9f80ecc6f5664
(cherry picked from commit 3b8257cd23)
(cherry picked from commit 4e5b92545d)

doc/source/cli/nova-status.rst

@@ -147,6 +147,8 @@ Upgrade
 
   * Checks for the policy files are not automatically overwritten with
     new defaults.
+  * Checks for computes older than the previous major release. This check was
+    backported from 23.0.0 (Wallaby).
 
 See Also
 ========

doc/source/install/verify.rst

@@ -127,3 +127,7 @@ Verify operation of the Compute service.
       | Result: Success                                                    |
       | Details: None                                                      |
       +--------------------------------------------------------------------+
+      | Check: Older than N-1 computes                                     |
+      | Result: Success                                                    |
+      | Details: None                                                      |
+      +--------------------------------------------------------------------+

nova/cmd/status.py

@@ -411,6 +411,17 @@ class UpgradeCommands(upgradecheck.UpgradeCommands):
         policy.reset()
         return status
 
+    def _check_old_computes(self):
+        # warn if there are computes in the system older than the previous
+        # major release
+        try:
+            utils.raise_if_old_compute()
+        except exception.TooOldComputeService as e:
+            return upgradecheck.Result(
+                upgradecheck.Code.WARNING, six.text_type(e))
+
+        return upgradecheck.Result(upgradecheck.Code.SUCCESS)
+
     # The format of the check functions is to return an upgradecheck.Result
     # object with the appropriate upgradecheck.Code and details set. If the
     # check hits warnings or failures then those should be stored in the
@@ -429,6 +440,8 @@ class UpgradeCommands(upgradecheck.UpgradeCommands):
         (_('Cinder API'), _check_cinder),
         # Added in Ussuri
         (_('Policy Scope-based Defaults'), _check_policy),
+        # Backported from Wallaby
+        (_('Older than N-1 computes'), _check_old_computes)
     )
 
 

nova/tests/unit/cmd/test_status.py

@@ -39,6 +39,7 @@ from nova import exception
 # NOTE(mriedem): We only use objects as a convenience to populate the database
 # in the tests, we don't use them in the actual CLI.
 from nova import objects
+from nova.objects import service
 from nova import policy
 from nova import test
 from nova.tests import fixtures as nova_fixtures
@@ -602,3 +603,32 @@ class TestUpgradeCheckPolicyEnableScope(TestUpgradeCheckPolicy):
     def setUp(self):
         super(TestUpgradeCheckPolicyEnableScope, self).setUp()
         self.flags(enforce_scope=True, group="oslo_policy")
+
+
+class TestUpgradeCheckOldCompute(test.NoDBTestCase):
+
+    def setUp(self):
+        super(TestUpgradeCheckOldCompute, self).setUp()
+        self.cmd = status.UpgradeCommands()
+
+    def test_no_compute(self):
+        self.assertEqual(
+            upgradecheck.Code.SUCCESS, self.cmd._check_old_computes().code)
+
+    def test_only_new_compute(self):
+        last_supported_version = service.SERVICE_VERSION_ALIASES[
+            service.OLDEST_SUPPORTED_SERVICE_VERSION]
+        with mock.patch(
+                "nova.objects.service.get_minimum_version_all_cells",
+                return_value=last_supported_version):
+            self.assertEqual(
+                upgradecheck.Code.SUCCESS, self.cmd._check_old_computes().code)
+
+    def test_old_compute(self):
+        too_old = service.SERVICE_VERSION_ALIASES[
+            service.OLDEST_SUPPORTED_SERVICE_VERSION] - 1
+        with mock.patch(
+                "nova.objects.service.get_minimum_version_all_cells",
+                return_value=too_old):
+            result = self.cmd._check_old_computes()
+            self.assertEqual(upgradecheck.Code.WARNING, result.code)