Takes contributor change suggested by filipenf:use-inventory-hostname,

README.md

@@ -24,8 +24,10 @@ Once the required libraries (see above) have been installed on the server:
 1. Copy `datadog_callback.py` to your playbook callback directory (by default
 `callback_plugins/` in your playbook's root directory). Create the directory
 if it doesn't exist.
-2. You have 3 ways to set your API key. The callback will first use the
-   environment variable, then the configuration file, then hostvars/vault.
+2. You have 4 ways to set your API key. The callback will first use the
+   environment variable, then the configuration file, then hostvars/vault,
+   and a specific host's hostvars.  For more information, see the environment
+   variable configuration.
 
 ##### Using environment variable
 
@@ -37,6 +39,11 @@ variable `DATADOG_SITE=datadoghq.eu`.
 To send data to a custom URL you can set the environment
 variable `DATADOG_URL=<custom URL>`.
 
+To configure the callback to use variables from a specific inventory host,
+you can set the environment variable `ANSIBLE_DATADOG_CALLBACK_INVENTORY_HOST`.
+The callback will then query that host's variables for the API key, datadog URL,
+and datadog site.
+
 ##### Using a yaml file
 
 Create a `datadog_callback.yml` file alongside `datadog_callback.py`,

datadog_callback.py

@@ -3,8 +3,10 @@
 import getpass
 import logging
 import os
+import socket
 import time
 
+
 try:
     import datadog
     import yaml
@@ -241,6 +243,25 @@ def v2_playbook_on_start(self, playbook):
             inventory = ','.join(inventory)
         self._inventory_name = ','.join([os.path.basename(os.path.realpath(name)) for name in inventory.split(',') if name])
 
+    def get_from_hostvars(self, variable_name, required=False):
+        hostvars = self.play.get_variable_manager()._hostvars
+        if not hostvars:
+            raise Exception("hostvars could not be loaded")
+        hosts = [ 'localhost', socket.gethostname() ]
+        if os.environ.get("ANSIBLE_DATADOG_CALLBACK_INVENTORY_HOST"):
+            hosts.insert(0, os.environ.get("ANSIBLE_DATADOG_CALLBACK_INVENTORY_HOST"))
+        for host in hosts:
+            if host not in hostvars:
+                continue
+            value = hostvars[host].get(variable_name, None)
+            if value is not None:
+                return value
+        if required:
+            raise Exception("variable {} is not defined in the host vars for hosts: {}".format(
+                variable_name, hosts))
+        else:
+            return None
+
     def v2_playbook_on_play_start(self, play):
         # On Ansible v2, Ansible doesn't set `self.play` automatically
         self.play = play
@@ -253,21 +274,17 @@ def v2_playbook_on_play_start(self, play):
 
         # If there is no api key defined in config file, try to get it from hostvars
         if api_key == '':
-            hostvars = self.play.get_variable_manager()._hostvars
-
-            if not hostvars:
-                print("No api_key found in the config file ({0}) and hostvars aren't set: disabling Datadog callback plugin".format(config_path))
+            try:
+                api_key = self.get_from_hostvars('datadog_api_key', True)
+                if not dd_url:
+                    dd_url = self.get_from_hostvars('datadog_url')
+
+                if not dd_site:
+                    dd_site = self.get_from_hostvars('datadog_site')
+            except Exception as e:
+                print('No "api_key" found in the config file ({0}) and could not load from the inventory ({1}): disabling Datadog callback plugin'.
+                        format(config_path, e))
                 self.disabled = True
-            else:
-                try:
-                    api_key = hostvars['localhost']['datadog_api_key']
-                    if not dd_url:
-                        dd_url = hostvars['localhost'].get('datadog_url')
-                    if not dd_site:
-                        dd_site = hostvars['localhost'].get('datadog_site')
-                except Exception as e:
-                    print('No "api_key" found in the config file ({0}) and "datadog_api_key" is not set in the hostvars: disabling Datadog callback plugin'.format(config_path))
-                    self.disabled = True
 
         if not dd_url:
             if dd_site: