Add an inventory config check option

Previously there was no way to do a 'dry run' against a set of inventory
configuration files without actually writing the full inventory
structure to disk.

This change adds a simple check flag to the script, allowing users to
pre-validate their configurations prior to executing the Ansible
playbooks. No syntax validation happens against the YAML files; rather,
the dynamic_inventory.py script is executed and builds a full inventory
in memory, but does not write any output.

Currently, this is meant as a starting point. Further validation can
build from here, but the flag is largely meant to check for known
exceptions/errors early.

Change-Id: Ic58566ee124c824c8bba549ade46bce5c268905a

doc/source/developer-docs/inventory.rst

@@ -101,6 +101,17 @@ The same JSON structure is printed to stdout, which is consumed by Ansible as
 the inventory for the playbooks.
 
 
+Checking Inventory Configuration for Errors
+-------------------------------------------
+
+Using the ``--check`` flag when running ``dynamic_inventory.py`` will run the
+inventory build process and look for known errors, but not write any files to
+disk.
+
+This check does not do YAML syntax validation, though it will fail if there
+are unparseable errors.
+
+
 Inspecting and Managing the Inventory
 -------------------------------------
 

playbooks/inventory/dynamic_inventory.py

@@ -133,6 +133,12 @@ def args(arg_list):
         action='store_true'
     )
 
+    parser.add_argument(
+        '--check',
+        help="Configuration check only, don't generate inventory",
+        action='store_true',
+    )
+
     return vars(parser.parse_args(arg_list))
 
 
@@ -1138,6 +1144,10 @@ def main(all_args):
         sort_keys=True
     )
 
+    check = all_args.get('check')
+    if check:
+        return 'Configuration ok!'
+
     # Generate a list of all hosts and their used IP addresses
     hostnames_ips = {}
     for _host, _vars in dynamic_inventory['_meta']['hostvars'].iteritems():

releasenotes/notes/config_check_argument-5a1126c779e3e8f5.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - The `dynamic_inventory.py` file now takes a new argument, ``--check``,
+    which will run the inventory build without writing any files to the file
+    system. This is useful for checking to make sure your configuration does
+    not contain known errors prior to running Ansible commands.
+

tests/test_inventory.py

@@ -737,7 +737,6 @@ class TestMultipleRuns(unittest.TestCase):
 
         inventory_file_path = os.path.join(TARGET_DIR,
                                            'openstack_inventory.json')
-
         inv = di.get_inventory(TARGET_DIR, inventory_file_path)
         self.assertIsInstance(inv, dict)
         self.assertIn('_meta', inv)
@@ -1001,5 +1000,22 @@ class TestSetUsedIPS(unittest.TestCase):
         di.USED_IPS = set()
 
 
+class TestConfigCheckFunctional(TestConfigCheckBase):
+    def duplicate_ip(self):
+        ip = self.user_defined_config['log_hosts']['aio1']
+        self.user_defined_config['log_hosts']['bogus'] = ip
+
+    def test_checking_good_config(self):
+        output = di.main({'config': TARGET_DIR, 'check': True})
+        self.assertEqual(output, 'Configuration ok!')
+
+    def test_duplicated_ip(self):
+        self.duplicate_ip()
+        self.write_config()
+        with self.assertRaises(di.MultipleHostsWithOneIPError) as context:
+            di.main({'config': TARGET_DIR, 'check': True})
+        self.assertEqual(context.exception.ip, '172.29.236.100')
+
+
 if __name__ == '__main__':
     unittest.main()