Make LoadBalancer nested stack template configurable

Reviving work originally posted by Angus Salkeld under
https://review.openstack.org/#/c/21405/

This is to enable the various distros to easily override the
hard-coded default nested template (which currently only supports
Fedora 17) with a template approporate to their distro, and
enables deployers to specify their own template (although the
latter use-case will probably be catered for via a provider
template implementation long-term).

Conflicts:
	heat/engine/resources/loadbalancer.py

Partial-Bug: #1234375
Co-Authored-By: Angus Salkeld <angus@salkeld.id.au>
(cherry picked from commit 746a0ed4ad2273d0e67b896efbb6d7a69f9f4c77)
Change-Id: I0a4eccb23b2eebbf31b7aabf0fe85ab31f0ca971

3 files changed, 54 insertions, 9 deletions

diff --git a/etc/heat/heat.conf.sample b/etc/heat/heat.conf.sample
index 1444f9ba2..ad6fb7cab 100644
--- a/etc/heat/heat.conf.sample
+++ b/etc/heat/heat.conf.sample
@@ -121,6 +121,15 @@
 
 
 #
+# Options defined in heat.engine.resources.loadbalancer
+#
+
+# Custom template for the built-in loadbalancer nested stack
+# (string value)
+#loadbalancer_template=<None>
+
+
+#
 # Options defined in heat.openstack.common.db.sqlalchemy.session
 #
 
diff --git a/heat/engine/resources/loadbalancer.py b/heat/engine/resources/loadbalancer.py
index 700158e06..7350d6cac 100644
--- a/heat/engine/resources/loadbalancer.py
+++ b/heat/engine/resources/loadbalancer.py
@@ -12,7 +12,11 @@
 #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 #    License for the specific language governing permissions and limitations
 #    under the License.
+import os
 
+from oslo.config import cfg
+
+from heat.common import exception
 from heat.common import template_format
 from heat.engine import stack_resource
 from heat.engine.resources import nova_utils
@@ -21,7 +25,7 @@ from heat.openstack.common import log as logging
 
 logger = logging.getLogger(__name__)
 
-lb_template = r'''
+lb_template_default = r'''
 {
   "AWSTemplateFormatVersion": "2010-09-09",
   "Description": "Built in HAProxy server",
@@ -189,11 +193,15 @@ lb_template = r'''
 '''
 
 
-#
-# TODO(asalkeld) the above inline template _could_ be placed in an external
-# file at the moment this is because we will probably need to implement a
-# LoadBalancer based on keepalived as well (for for ssl support).
-#
+# Allow user to provide alternative nested stack template to the above
+loadbalancer_opts = [
+    cfg.StrOpt('loadbalancer_template',
+               default=None,
+               help='Custom template for the built-in '
+                    'loadbalancer nested stack')]
+cfg.CONF.register_opts(loadbalancer_opts)
+
+
 class LoadBalancer(stack_resource.StackResource):
 
     listeners_schema = {
@@ -361,8 +369,18 @@ class LoadBalancer(stack_resource.StackResource):
 
         return '%s%s%s%s\n' % (gl, frontend, backend, '\n'.join(servers))
 
+    def get_parsed_template(self):
+        if cfg.CONF.loadbalancer_template:
+            with open(cfg.CONF.loadbalancer_template) as templ_fd:
+                logger.info(_('Using custom loadbalancer template %s')
+                            % cfg.CONF.loadbalancer_template)
+                contents = templ_fd.read()
+        else:
+            contents = lb_template_default
+        return template_format.parse(contents)
+
     def handle_create(self):
-        templ = template_format.parse(lb_template)
+        templ = self.get_parsed_template()
 
         if self.properties['Instances']:
             md = templ['Resources']['LB_instance']['Metadata']
@@ -388,7 +406,7 @@ class LoadBalancer(stack_resource.StackResource):
         rely on the cfn-hup to reconfigure HAProxy
         '''
         if 'Instances' in prop_diff:
-            templ = template_format.parse(lb_template)
+            templ = self.get_parsed_template()
             cfg = self._haproxy_config(templ, prop_diff['Instances'])
 
             md = self.nested()['LB_instance'].metadata
@@ -408,6 +426,11 @@ class LoadBalancer(stack_resource.StackResource):
         if res:
             return res
 
+        if cfg.CONF.loadbalancer_template and \
+                not os.access(cfg.CONF.loadbalancer_template, os.R_OK):
+            msg = _('Custom LoadBalancer template can not be found')
+            raise exception.StackValidationFailed(message=msg)
+
         health_chk = self.properties['HealthCheck']
         if health_chk:
             if float(health_chk['Interval']) < float(health_chk['Timeout']):
diff --git a/heat/tests/test_loadbalancer.py b/heat/tests/test_loadbalancer.py
index 843edb27f..aa07bb87f 100644
--- a/heat/tests/test_loadbalancer.py
+++ b/heat/tests/test_loadbalancer.py
@@ -179,8 +179,9 @@ class LoadBalancerTest(HeatTestCase):
 
         self.assertEqual('LoadBalancer', rsrc.FnGetRefId())
 
-        templ = template_format.parse(lb.lb_template)
+        templ = template_format.parse(lb.lb_template_default)
         ha_cfg = rsrc._haproxy_config(templ, rsrc.properties['Instances'])
+
         self.assertRegexpMatches(ha_cfg, 'bind \*:80')
         self.assertRegexpMatches(ha_cfg, 'server server1 1\.2\.3\.4:80 '
                                  'check inter 30s fall 5 rise 3')
@@ -228,3 +229,15 @@ class LoadBalancerTest(HeatTestCase):
             msg = '%s: %r not found in %r' % (msg,
                                               expected_regexp.pattern, text)
             raise self.failureException(msg)
+
+    def test_loadbalancer_validate_badtemplate(self):
+        cfg.CONF.set_override('loadbalancer_template', '/a/noexist/x.y')
+
+        t = template_format.parse(lb_template)
+        s = utils.parse_stack(t)
+        s.store()
+
+        rsrc = lb.LoadBalancer('LoadBalancer',
+                               t['Resources']['LoadBalancer'],
+                               s)
+        self.assertRaises(exception.StackValidationFailed, rsrc.validate)