Merge pull request #1224 from alphagov/celery_logging

log unhandled celery exceptions

app/celery/celery.py

@@ -1,17 +1,28 @@
-from celery import Celery
+from flask import current_app
+from celery import Celery, Task
+
+
+class NotifyTask(Task):
+    abstract = True
+
+    def on_failure(self, exc, task_id, args, kwargs, einfo):
+        # ensure task will log exceptions to correct handlers
+        current_app.logger.exception('Celery task failed')
+        super().on_failure(exc, task_id, args, kwargs, einfo)
+
+    def __call__(self, *args, **kwargs):
+        # ensure task has flask context to access config, logger, etc
+        with current_app.app_context():
+            return super().__call__(*args, **kwargs)
 
 
 class NotifyCelery(Celery):
 
     def init_app(self, app):
-        super().__init__(app.import_name, broker=app.config['BROKER_URL'])
+        super().__init__(
+            app.import_name,
+            broker=app.config['BROKER_URL'],
+            task_cls=NotifyTask,
+        )
+
         self.conf.update(app.config)
-        TaskBase = self.Task
-
-        class ContextTask(TaskBase):
-            abstract = True
-
-            def __call__(self, *args, **kwargs):
-                with app.app_context():
-                    return TaskBase.__call__(self, *args, **kwargs)
-        self.Task = ContextTask