From e5cbbcfc6a5fa31565d21e6c0ea260faca3b253d Mon Sep 17 00:00:00 2001
From: Dan Smith <danms@us.ibm.com>
Date: Wed, 6 Feb 2013 11:26:59 -0500
Subject: [PATCH] Ban database access in nova-compute

This adds a wedge between nova-compute and the database implementation
to specifically catch, log, and deny accesses. Theoretically, this
should not be needed as a production environment would not even have
the compute nodes configured to talk to the database. However, testing
and upgraded environments may retain database access and thus avoid
hitting real issues that can be fixed up prior to release. Putting
this into the tree now will help ensure we have a consistent error
scenario for test setups prior to release.

Note that if nova is configured to use a local conductor, we do not
insert the wedge, which provides an easy out for anyone needing to
get a production system past a missed database access.

Related to bp no-db-compute.

Based on Russell's original tracer hack:

   I328fa92d5bfdadd5022f5c7efe981396d8ae7962

Change-Id: I478230220633e0d2ff94b6a4d756e07eab8517d7
---
 bin/nova-compute | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/bin/nova-compute b/bin/nova-compute
index 8826015d4104..814147d66328 100755
--- a/bin/nova-compute
+++ b/bin/nova-compute
@@ -31,6 +31,7 @@ else:
 
 import os
 import sys
+import traceback
 
 # If ../nova/__init__.py exists, add ../ to Python search path, so that
 # it will override what happens to be installed in /usr/(local/)lib/python...
@@ -42,6 +43,8 @@ if os.path.exists(os.path.join(POSSIBLE_TOPDIR, 'nova', '__init__.py')):
 
 
 from nova import config
+import nova.db.api
+from nova import exception
 from nova.openstack.common import cfg
 from nova.openstack.common import log as logging
 from nova import service
@@ -49,11 +52,31 @@ from nova import utils
 
 CONF = cfg.CONF
 CONF.import_opt('compute_topic', 'nova.compute.rpcapi')
+CONF.import_opt('use_local', 'nova.conductor.api', group='conductor')
+LOG = logging.getLogger('nova.compute')
+
+
+def block_db_access():
+    class NoDB(object):
+        def __getattr__(self, attr):
+            return self
+
+        def __call__(self, *args, **kwargs):
+            stacktrace = "".join(traceback.format_stack())
+            LOG.error('No db access allowed in nova-compute: %s' % stacktrace)
+            raise exception.DBError('No db access allowed in nova-compute')
+
+    nova.db.api.IMPL = NoDB()
+
 
 if __name__ == '__main__':
     config.parse_args(sys.argv)
     logging.setup('nova')
     utils.monkey_patch()
+
+    if not CONF.conductor.use_local:
+        block_db_access()
+
     server = service.Service.create(binary='nova-compute',
                                     topic=CONF.compute_topic,
                                     db_allowed=False)