Allow to override celery config file name via the SWH_CONFIG_FILENAME env var

this will take precedence over the implicit config file scheme. The expected config file given via the environment variable is expected to have a [celery] section which will be used as config for the Celery app created in swh.scheduler.celery_backend.config.

Related to swh-core#1410 and swh-core#826 (closed).

---

Migrated from D1067 (view on Phabricator)

swh/scheduler/celery_backend/config.py

@@ -190,13 +190,24 @@ def register_task_class(app, name, cls):
 
 
 INSTANCE_NAME = os.environ.get(CONFIG_NAME_ENVVAR)
-if INSTANCE_NAME:
-    CONFIG_NAME = CONFIG_NAME_TEMPLATE % INSTANCE_NAME
-else:
-    CONFIG_NAME = DEFAULT_CONFIG_NAME
-
-# Load the Celery config
-CONFIG = load_named_config(CONFIG_NAME, DEFAULT_CONFIG)
+CONFIG_NAME = os.environ.get('SWH_CONFIG_FILENAME')
+CONFIG = {}
+if CONFIG_NAME:
+    # load the celery config from the main config file given as
+    # SWH_CONFIG_FILENAME environment variable.
+    # This is expected to have a [celery] section in which we have the
+    # celery specific configuration.
+    CONFIG = load_named_config(CONFIG_NAME).get('celery')
+
+if not CONFIG:
+    # otherwise, back to compat config loading mechanism
+    if INSTANCE_NAME:
+        CONFIG_NAME = CONFIG_NAME_TEMPLATE % INSTANCE_NAME
+    else:
+        CONFIG_NAME = DEFAULT_CONFIG_NAME
+
+    # Load the Celery config
+    CONFIG = load_named_config(CONFIG_NAME, DEFAULT_CONFIG)
 
 # Celery Queues
 CELERY_QUEUES = [Queue('celery', Exchange('celery'), routing_key='celery')]
@@ -206,7 +217,7 @@ CELERY_DEFAULT_CONFIG = dict(
     enable_utc=True,
     timezone='UTC',
     # Imported modules
-    imports=CONFIG['task_modules'],
+    imports=CONFIG.get('task_modules', []),
     # Time (in seconds, or a timedelta object) for when after stored task
     # tombstones will be deleted. None means to never expire results.
     result_expires=None,
@@ -235,14 +246,6 @@ CELERY_DEFAULT_CONFIG = dict(
     # (Disabling rate limits altogether is recommended if you don’t have any
     # tasks using them.)
     worker_disable_rate_limits=True,
-    # Task hard time limit in seconds. The worker processing the task will be
-    # killed and replaced with a new one when this is exceeded.
-    # task_time_limit=3600,
-    # Task soft time limit in seconds.
-    # The SoftTimeLimitExceeded exception will be raised when this is exceeded.
-    # The task can catch this to e.g. clean up before the hard time limit
-    # comes.
-    task_soft_time_limit=CONFIG['task_soft_time_limit'],
     # Task routing
     task_routes=route_for_task,
     # Task queues this worker will consume from