[GitHub] [airflow] mik-laj commented on a change in pull request #6247: [AIRFLOW-5588] Add Celery's architecture diagram

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mik-laj commented on a change in pull request #6247: [AIRFLOW-5588] Add Celery's architecture diagram
URL: https://github.com/apache/airflow/pull/6247#discussion_r333026452
 
 

 ##########
 File path: docs/executor/celery.rst
 ##########
 @@ -72,3 +72,74 @@ Some caveats:
 - Make sure to set a visibility timeout in [celery_broker_transport_options] that exceeds the ETA of your longest running task
 - Tasks can consume resources. Make sure your worker has enough resources to run ``worker_concurrency`` tasks
 - Queue names are limited to 256 characters, but each broker backend might have its own restrictions
+
+Architecture
+------------
+
+.. graphviz::
+
+    digraph A{
+        rankdir="TB"
+        node[shape="rectangle", style="rounded"]
+
+
+        subgraph cluster {
+            label="Cluster";
+            {rank = same; dag; database}
+            {rank = same; workers; scheduler; web}
+
+            workers[label="Workers"]
+            scheduler[label="Scheduler"]
+            web[label="Web server"]
+            database[label="Database"]
+            dag[label="DAG files"]
+
+            subgraph cluster_queue {
+                label="Queue";
+                {rank = same; queue_broker; queue_result_backend}
+                queue_broker[label="Queue broker"]
+                queue_result_backend[label="Result backend"]
+            }
+
+            scheduler->workers[label="1"]
+            web->database[label="2"]
+            web->dag[label="3"]
+
+            workers->database[label="4"]
+            workers->dag[label="5"]
+            workers->queue_result_backend[label="6"]
+            workers->queue_broker[label="7"]
+
+            scheduler->database[label="8"]
+            scheduler->dag[label="9"]
+            scheduler->queue_result_backend[label="10"]
+            scheduler->queue_broker[label="11"]
+        }
+    }
+
+Airflow consist of several components:
+
+* **Workers** - Execute the assigned tasks
+* **Scheduler** - Responsible for adding the necessary tasks to the queue
+* **Web server** - Server HTTP provides access to DAG/task status information
+* **Database** - Contains information about the status of tasks, DAGs, Variables, connections, etc.
+* **Queue** - Queue mechanism provided by Celery
+
+Please note that the queue at Celery consists of two components:
+
+* **Broker** - Stores commands for execution
+* **Result backend** - Stores status of completed command
+
+The components communicate with each other in many places
+
+* [1] **Scheduler** --> **Workers** - Fetchs task execution logs
 
 Review comment:
   I checked it out. This is true. Webserver fetches logs.
   https://github.com/apache/airflow/blob/d719e1f/airflow/www/views.py#L554-L572
   https://github.com/apache/airflow/blob/d719e1fd6705a93a0dfefef4b46478ade5e006ea/airflow/utils/log/file_task_handler.py#L110-L132 
   I updated tihis PR.
   

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