Add a check for legacy hiera element data

The new heat 'hiera' hook is incompatible with the old
tripleo-puppet-elements hiera element. The two formats
should not coexist as they will overwrite each others
config files (last hook to run would win).

To make the end user experience nice we add an explicit check
here. Note: this would require us to clean out old
apply-config data from a prior run during an upgrade to make
sure the check doesn't mistakenly prevent a new deployment
from failing.

Change-Id: I326a2816b6c47b2ba00c33a42ce6e452c5a74dce

heat-config-hiera/install.d/hook-hiera.py

@@ -15,12 +15,18 @@
 import json
 import logging
 import os
+import subprocess
 import sys
 
 
 HIERA_DATADIR = os.environ.get('HEAT_PUPPET_HIERA_DATADIR',
                                '/etc/puppet/hieradata')
 HIERA_CONFIG = os.environ.get('HEAT_HIERA_CONFIG', '/etc/puppet/hiera.yaml')
+HIERA_ELEMENT_CHECK_CMD = os.environ.get('HEAT_HIERA_ELEMENT_CHECK_CMD',
+                                         'os-apply-config '
+                                         '--key hiera.datafiles '
+                                         '--type raw --key-default empty')
+
 
 HIERA_CONFIG_BASE = """
 ---
@@ -37,6 +43,31 @@ def prepare_dir(path):
         os.makedirs(path, 0o700)
 
 
+def exit_legacy_hiera_detected():
+    try:
+        subproc = subprocess.Popen(HIERA_ELEMENT_CHECK_CMD.split(" "),
+                                   stdout=subprocess.PIPE,
+                                   stderr=subprocess.PIPE)
+        stdout, stderr = subproc.communicate()
+        if stdout.rstrip() != 'empty':
+            err_msg = ('Legacy hieradata from os-apply-config has been '
+                       'detected. Please update all of your interfaces '
+                       'to use the new heat-agents hiera hook before '
+                       'proceeding')
+            response = {
+                'deploy_stdout': stdout,
+                'deploy_stderr': err_msg,
+                'deploy_status_code': 1,
+            }
+
+            json.dump(response, sys.stdout)
+            sys.exit(0)
+
+    except OSError:
+        # os-apply-config is not installed? Assume there is no legacy data.
+        pass
+
+
 def main(argv=sys.argv):
     log = logging.getLogger('heat-config')
     handler = logging.StreamHandler(sys.stderr)
@@ -47,6 +78,7 @@ def main(argv=sys.argv):
     log.setLevel('DEBUG')
 
     c = json.load(sys.stdin)['config']
+    exit_legacy_hiera_detected()
 
     prepare_dir(HIERA_DATADIR)