callbacks: Add ntfy callback plugin

This plugin sends a notification using _ntfy_ whenever a playbook
fails.  This will be useful especially for automated deployments when
the playbook was not launched manually.

.gitignore

@@ -5,3 +5,5 @@
 /victoria-metrics-*.tar.gz
 /victoria-metrics-*/
 /tmp/
+__pycache__/
+*.py[co]

ansible.cfg

@@ -3,6 +3,8 @@
 [defaults]
 inventory = hosts
 
+callback_plugins = plugins/callback
+
 gathering = smart
 fact_caching = jsonfile
 fact_caching_connection = .fact-cache
@@ -10,3 +12,6 @@ fact_caching_connection = .fact-cache
 force_valid_group_names = ignore
 
 remote_tmp = /var/tmp
+
+[callback_ntfy]
+server = https://ntfy.pyrocufflink.blue

plugins/callback/ntfy.py

@@ -0,0 +1,94 @@
+from pathlib import Path
+import urllib.request
+
+from ansible.errors import AnsibleError
+from ansible.executor.stats import AggregateStats
+from ansible.playbook import Playbook
+from ansible.plugins.callback import CallbackBase
+
+
+DOCUMENTATION = r'''
+author: Dustin C. Hatch
+name: ntfy
+short_description: Send notifications to ntfy.sh
+description:
+- This plugin sends playbook failure notifications via ntfy.sh.
+options:
+  server:
+    description: ntfy.sh server
+    type: str
+    default: https://ntfy.sh
+    env:
+    - name: NTFY_SERVER
+    ini:
+    - section: callback_ntfy
+      key: server
+  topic:
+    description: ntfy.sh topic name
+    type: str
+    default: ansible
+    env:
+    - name: NTFY_TOPIC
+    ini:
+    - section: callback_ntfy
+      key: topic
+'''
+
+
+class CallbackModule(CallbackBase):
+    CALLBACK_VERSION = 1.0
+    CALLBACK_TYPE = 'notification'
+    CALLBACK_NAME = 'ntfy'
+
+    def __init__(self):
+        super().__init__()
+        self.playbook = None
+
+    def set_options(self, task_keys=None, var_options=None, direct=None):
+        super().set_options(task_keys, var_options, direct)
+        ntfy_server = self.get_option('server').rstrip('/')
+        if '://' not in ntfy_server:
+            ntfy_server = f'http://{ntfy_server}'
+        ntfy_topic = self.get_option('topic')
+        self.ntfy_url = f'{ntfy_server}/{ntfy_topic}'
+
+    def v2_playbook_on_start(self, playbook: Playbook):
+        self.playbook = playbook
+
+    def v2_playbook_on_stats(self, stats: AggregateStats):
+        if not self.playbook:
+            return
+        if not stats.failures and not stats.dark:
+            return
+        assert self.playbook._file_name
+        playbook = Path(self.playbook._file_name)
+        results = {}
+        hosts = set(stats.failures.keys()).union(stats.dark.keys())
+        title = f'Playbook {playbook.name} failed for {len(hosts)} hosts'
+        for host in hosts:
+            results[host] = {
+                'ok': stats.ok.get(host, 0),
+                'changed': stats.changed.get(host, 0),
+                'unreachable': stats.dark.get(host, 0),
+                'failed': stats.failures.get(host, 0),
+                'skipped': stats.skipped.get(host, 0),
+                'rescued': stats.rescued.get(host, 0),
+                'ignored': stats.ignored.get(host, 0),
+            }
+        lines = []
+        for host, result in results.items():
+            result_txt = ' '.join(f'{k}={v}' for k, v in result.items())
+            lines.append(f'{host} : {result_txt}')
+        message = '\n'.join(lines)
+        req = urllib.request.Request(
+            self.ntfy_url,
+            method='POST',
+            data=message.encode('utf-8'),
+        )
+        req.add_header('Title', title)
+        req.add_header('Tag', 'red_circle')
+        with urllib.request.urlopen(req) as response:
+            status_code = response.getcode()
+            if status_code < 200 or status_code >= 300:
+                response_data = response.read()
+                raise AnsibleError(f'Failed to send notification: {response_data.decode()}')