Isolate cluster-dependent Celery startup

Avoids calling unworkable functions when generating API docs etc. by
isolating them into a Celery startup function called by Daemon.py.

Also update to Celery 4+ settings format.

api-daemon/pvcapid/Daemon.py

@@ -155,6 +155,7 @@ def entrypoint():
     print("|----------------------------------------------------------|")
     print("")
 
+    pvc_api.celery_startup()
     pvc_api.app.run(
         config["listen_address"],
         config["listen_port"],

api-daemon/pvcapid/flaskapi.py

@@ -57,64 +57,6 @@ from flask_sqlalchemy import SQLAlchemy
 
 # Create Flask app and set config values
 app = flask.Flask(__name__)
-celery_task_uri = "redis://{}:{}{}".format(
-    config["queue_host"], config["queue_port"], config["queue_path"]
-)
-app.config["CELERY_BROKER_URL"] = celery_task_uri
-app.config["CELERY_RESULT_BACKEND"] = celery_task_uri
-
-
-# Set up Celery queues
-@ZKConnection(config)
-def get_all_nodes(zkhandler):
-    _, all_nodes = get_node_list(zkhandler, None)
-    return [n["name"] for n in all_nodes]
-
-
-@ZKConnection(config)
-def get_primary_node(zkhandler):
-    return getPrimaryNode(zkhandler)
-
-
-app.config["CELERY_QUEUES"] = tuple(
-    [Queue(h, routing_key=f"{h}.#") for h in get_all_nodes()]
-)
-
-
-# Set up Celery queue routing
-def route_task(name, args, kwargs, options, task=None, **kw):
-    print("----")
-    print(f"Incoming Celery task: '{name}' with args {args}, kwargs {kwargs}")
-
-    # If an explicit routing_key is set and it's in the kwargs of the function, use it to set the queue
-    if options["routing_key"] != "default" and options["routing_key"] in kwargs.keys():
-        run_on = kwargs[options["routing_key"]]
-        if run_on == "primary":
-            run_on = get_primary_node()
-    # Otherwise, use the primary node
-    else:
-        run_on = get_primary_node()
-
-    print(f"Selected Celery worker: {run_on}")
-    print("----")
-
-    return run_on
-
-
-app.config["CELERY_ROUTES"] = (route_task,)
-
-
-# Set up Celery task ID generator
-# WHY? We don't want to use UUIDs; they're too long and cumbersome. Instead, use a shorter partial UUID.
-def run_celery_task(task_def, **kwargs):
-    task_id = str(uuid4()).split("-")[0]
-    task = task_def.apply_async(
-        (),
-        kwargs,
-        task_id=task_id,
-    )
-    return task
-
 
 # Set up SQLAlchemy backend
 app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
@@ -144,14 +86,72 @@ blueprint = flask.Blueprint("api", __name__, url_prefix="/api/v1")
 api = Api(blueprint)
 app.register_blueprint(blueprint)
 
+
+# Set up Celery queues
+@ZKConnection(config)
+def get_all_nodes(zkhandler):
+    _, all_nodes = get_node_list(zkhandler, None)
+    return [n["name"] for n in all_nodes]
+
+
+@ZKConnection(config)
+def get_primary_node(zkhandler):
+    return getPrimaryNode(zkhandler)
+
+
+# Set up Celery queue routing
+def route_task(name, args, kwargs, options, task=None, **kw):
+    print("----")
+    print(f"Incoming Celery task: '{name}' with args {args}, kwargs {kwargs}")
+
+    # If an explicit routing_key is set and it's in the kwargs of the function, use it to set the queue
+    if options["routing_key"] != "default" and options["routing_key"] in kwargs.keys():
+        run_on = kwargs[options["routing_key"]]
+        if run_on == "primary":
+            run_on = get_primary_node()
+    # Otherwise, use the primary node
+    else:
+        run_on = get_primary_node()
+
+    print(f"Selected Celery worker: {run_on}")
+    print("----")
+
+    return run_on
+
+
+# Set up Celery task ID generator
+# WHY? We don't want to use UUIDs; they're too long and cumbersome. Instead, use a shorter partial UUID.
+def run_celery_task(task_def, **kwargs):
+    task_id = str(uuid4()).split("-")[0]
+    task = task_def.apply_async(
+        (),
+        kwargs,
+        task_id=task_id,
+    )
+    return task
+
+
 # Create celery definition
+celery_task_uri = "redis://{}:{}{}".format(
+    config["queue_host"], config["queue_port"], config["queue_path"]
+)
 celery = Celery(
     app.name,
     broker=celery_task_uri,
     result_backend=celery_task_uri,
     result_extended=True,
 )
-celery.conf.update(app.config)
+
+
+def celery_startup():
+    app.config["CELERY_broker_url"] = celery_task_uri
+    app.config["result_backend"] = celery_task_uri
+    app.config["task_queues"] = tuple(
+        [Queue(h, routing_key=f"{h}.#") for h in get_all_nodes()]
+    )
+    app.config["task_routes"] = (route_task,)
+    celery.conf.update(app.config)
+
 
 #
 # Custom decorators