inconsistent memcached cache caused tempest failure

[norman shen]

We are facing with following errors

test_role_create_update_show_list[id-18afc6c0-46cf-4911-824e-9989cc056c3a,smoke]

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/dist-packages/tempest/api/identity/admin/v3/test_roles.py", line 93, in test_role_create_update_show_list
    self.assertEqual(new_name, new_role['name'])
  File "/usr/local/lib/python3.6/dist-packages/testtools/testcase.py", line 411, in assertEqual
    self.assertThat(observed, matcher, message)
  File "/usr/local/lib/python3.6/dist-packages/testtools/testcase.py", line 498, in assertThat
    raise mismatch_error
testtools.matchers._impl.MismatchError: 'tempest-NewRole-1621384106' != 'tempest-Role-1980796659'

I am confident this error is caused by inconsistent cache, because it disappears when I set replicas of memcached deployment to be 1.

Because in nature memcached is not clustered, I think it will be appropriate to use statefulset and headerless service.