Add ability to rename host inventory variables using patterns

Certain environments may have conflicts with the variables given by
Netbox, and the variables used in the existing Ansible codebase.

With this change, such cases can be worked around by renaming individual
variables, or whole groups of them.

For example, this will rename all `cluster*` variables to have a
`netbox__` prefix instead (e.g., `cluster_group` -> `netbox__cluster_group`):

```yaml
rename_variables:
  - pattern: 'cluster(.*)'
    repl: 'netbox__cluster\1'
```

Uses a list, instead of a dict, to ensure that the order of evaluation
is strictly defined across all Python versions, and to add the ability
to exclude certain variables from being rewritten. For example:

```yaml
rename_variables:
  # Keep cluster_type the same
  - pattern: 'cluster_type'
    repl: 'cluster_type'

  # Rename all other cluster* variables
  - pattern: 'cluster(.*)'
    repl: 'netbox__cluster\1'
```

plugins/inventory/nb_inventory.py

@@ -3,6 +3,8 @@
 
 from __future__ import absolute_import, division, print_function
 
+import re
+
 __metaclass__ = type
 
 DOCUMENTATION = """
@@ -249,6 +251,15 @@
             description: Use out of band IP as `ansible host`
             type: boolean
             default: false
+        rename_variables:
+            description:
+                - Rename variables evaluated by nb_inventory, before writing them.
+                - Each list entry contains a dict with a 'pattern' and a 'repl'.
+                - Both 'pattern' and 'repl' are regular expressions.
+                - The first matching expression is used, subsequent matches are ignored.
+                - Internally `re.sub` is used.
+            type: list
+            defaut: []
 """
 
 EXAMPLES = """
@@ -1905,31 +1916,37 @@ def _setup_nested_groups(self, group, lookup, parent_lookup):
 
         return transformed_group_names
 
+    def _set_variable(self, hostname, key, value):
+        for item in self.rename_variables:
+            if item["pattern"].match(key):
+                key = item["pattern"].sub(item["repl"], key)
+                break
+
+        self.inventory.set_variable(hostname, key, value)
+
     def _fill_host_variables(self, host, hostname):
         extracted_primary_ip = self.extract_primary_ip(host=host)
         if extracted_primary_ip:
-            self.inventory.set_variable(hostname, "ansible_host", extracted_primary_ip)
+            self._set_variable(hostname, "ansible_host", extracted_primary_ip)
 
         if self.ansible_host_dns_name:
             extracted_dns_name = self.extract_dns_name(host=host)
             if extracted_dns_name:
-                self.inventory.set_variable(
-                    hostname, "ansible_host", extracted_dns_name
-                )
+                self._set_variable(hostname, "ansible_host", extracted_dns_name)
 
         extracted_primary_ip4 = self.extract_primary_ip4(host=host)
         if extracted_primary_ip4:
-            self.inventory.set_variable(hostname, "primary_ip4", extracted_primary_ip4)
+            self._set_variable(hostname, "primary_ip4", extracted_primary_ip4)
 
         extracted_primary_ip6 = self.extract_primary_ip6(host=host)
         if extracted_primary_ip6:
-            self.inventory.set_variable(hostname, "primary_ip6", extracted_primary_ip6)
+            self._set_variable(hostname, "primary_ip6", extracted_primary_ip6)
 
         extracted_oob_ip = self.extract_oob_ip(host=host)
         if extracted_oob_ip:
-            self.inventory.set_variable(hostname, "oob_ip", extracted_oob_ip)
+            self._set_variable(hostname, "oob_ip", extracted_oob_ip)
             if self.oob_ip_as_primary_ip:
-                self.inventory.set_variable(hostname, "ansible_host", extracted_oob_ip)
+                self._set_variable(hostname, "ansible_host", extracted_oob_ip)
 
         for attribute, extractor in self.group_extractors.items():
             extracted_value = extractor(host)
@@ -1965,9 +1982,9 @@ def _fill_host_variables(self, host, hostname):
                 )
             ):
                 for key, value in extracted_value.items():
-                    self.inventory.set_variable(hostname, key, value)
+                    self._set_variable(hostname, key, value)
             else:
-                self.inventory.set_variable(hostname, attribute, extracted_value)
+                self._set_variable(hostname, attribute, extracted_value)
 
     def _get_host_virtual_chassis_master(self, host):
         virtual_chassis = host.get("virtual_chassis", None)
@@ -2146,4 +2163,15 @@ def parse(self, inventory, loader, path, cache=True):
         self.ansible_host_dns_name = self.get_option("ansible_host_dns_name")
         self.racks = self.get_option("racks")
 
+        # Compile regular expressions, if any
+        self.rename_variables = self.parse_rename_variables(
+            self.get_option("rename_variables")
+        )
+
         self.main()
+
+    def parse_rename_variables(self, rename_variables):
+        return [
+            {"pattern": re.compile(i["pattern"]), "repl": i["repl"]}
+            for i in rename_variables or ()
+        ]

tests/unit/inventory/test_nb_inventory.py

@@ -34,6 +34,18 @@
 )
 
 
+class MockInventory:
+
+    def __init__(self):
+        self.variables = {}
+
+    def set_variable(self, hostname, key, value):
+        if hostname not in self.variables:
+            self.variables[hostname] = {}
+
+        self.variables[hostname][key] = value
+
+
 @pytest.fixture
 def inventory_fixture(
     allowed_device_query_parameters_fixture, allowed_vm_query_parameters_fixture
@@ -46,6 +58,9 @@ def inventory_fixture(
     inventory.allowed_device_query_parameters = allowed_device_query_parameters_fixture
     inventory.allowed_vm_query_parameters = allowed_vm_query_parameters_fixture
 
+    # Inventory mock, to validate what has been set via inventory.inventory.set_variable
+    inventory.inventory = MockInventory()
+
     return inventory
 
 
@@ -260,3 +275,22 @@ def test_extract_custom_fields(inventory_fixture, custom_fields, expected):
     )
 
     assert extracted_custom_fields == expected
+
+
+def test_rename_variables(inventory_fixture):
+    inventory_fixture.rename_variables = inventory_fixture.parse_rename_variables((
+        {"pattern": r"cluster(.*)", "repl": r'netbox_cluster\1'},
+        {"pattern": r"ansible_host", "repl": r"host"},
+    ))
+
+    inventory_fixture._set_variable("host", "ansible_fqdn", "host.example.org")
+    inventory_fixture._set_variable("host", "ansible_host", "host")
+    inventory_fixture._set_variable("host", "cluster", "staging")
+    inventory_fixture._set_variable("host", "cluster_id", "0xdeadbeef")
+
+    assert inventory_fixture.inventory.variables["host"] == {
+        "ansible_fqdn": "host.example.org",
+        "host": "host",
+        "netbox_cluster": "staging",
+        "netbox_cluster_id": "0xdeadbeef"
+    }