[AIRFLOW-966] Make celery broker_transport_options configurable

Required for changing visibility timeout and other options required
for Redis/SQS.

airflow/config_templates/default_airflow.cfg

@@ -310,6 +310,13 @@ default_queue = default
 # Import path for celery configuration options
 celery_config_options = airflow.config_templates.default_celery.DEFAULT_CELERY_CONFIG
 
+[celery_broker_transport_options]
+# The visibility timeout defines the number of seconds to wait for the worker
+# to acknowledge the task before the message is redelivered to another worker.
+# Make sure to increase the visibility timeout to match the time of the longest
+# ETA you’re planning to use. Especially important in case of using Redis or SQS
+visibility_timeout = 21600
+
 [dask]
 # This section only applies if you are using the DaskExecutor in
 # [core] section above

airflow/config_templates/default_celery.py

@@ -19,6 +19,10 @@
 from airflow.utils.log.logging_mixin import LoggingMixin
 
 
+broker_transport_options = configuration.getsection('celery_broker_transport_options')
+if broker_transport_options is None:
+    broker_transport_options = {'visibility_timeout': 21600}
+
 DEFAULT_CELERY_CONFIG = {
     'accept_content': ['json', 'pickle'],
     'event_serializer': 'json',
@@ -28,7 +32,7 @@
     'task_default_queue': configuration.get('celery', 'DEFAULT_QUEUE'),
     'task_default_exchange': configuration.get('celery', 'DEFAULT_QUEUE'),
     'broker_url': configuration.get('celery', 'BROKER_URL'),
-    'broker_transport_options': {'visibility_timeout': 21600},
+    'broker_transport_options': {'visibility_timeout': broker_transport_options},
     'result_backend': configuration.get('celery', 'CELERY_RESULT_BACKEND'),
     'worker_concurrency': configuration.getint('celery', 'CELERYD_CONCURRENCY'),
 }

airflow/configuration.py

@@ -236,6 +236,12 @@ def read(self, filenames):
         ConfigParser.read(self, filenames)
         self._validate()
 
+    def getsection(self, section):
+        if section in self._sections:
+            return self._sections[section]
+
+        return None
+
     def as_dict(self, display_source=False, display_sensitive=False):
         """
         Returns the current configuration as an OrderedDict of OrderedDicts.
@@ -423,6 +429,10 @@ def getint(section, key):
     return conf.getint(section, key)
 
 
+def getsection(section):
+    return conf.getsection(section)
+
+
 def has_option(section, key):
     return conf.has_option(section, key)
 

docs/configuration.rst

@@ -155,6 +155,11 @@ Note that you can also run "Celery Flower", a web UI built on top of Celery,
 to monitor your workers. You can use the shortcut command ``airflow flower``
 to start a Flower web server.
 
+Some caveats:
+
+- Make sure to use a database backed result backend
+- Make sure to set a visibility timeout in [celery_broker_transport_options] that exceeds the ETA of your longest running task
+- Tasks can and consume resources, make sure your worker as enough resources to run `celeryd_concurrency` tasks
 
 Scaling Out with Dask
 '''''''''''''''''''''