Warn on Webserver when using SQLite or SequentialExecutor (#1…

…7133)

Context: https://lists.apache.org/thread.html/r07e83f2462f08c4a52f6428b771a07e067ce9272b6256dca470a87fc%40%3Cdev.airflow.apache.org%3E
Note: Red flashes are for errors, we shouldn't use that.
GitOrigin-RevId: cb6fdd7495c3888fff3a4553af75aaf22bf95fa7

airflow/www/views.py

@@ -512,6 +512,30 @@ def health(self):
     )
     def index(self):
         """Home view."""
+        unit_test_mode: bool = conf.getboolean('core', 'UNIT_TEST_MODE')
+
+        if not unit_test_mode and "sqlite" in conf.get("core", "sql_alchemy_conn"):
+            db_doc_page = get_docs_url("howto/set-up-database.html")
+            flash(
+                Markup(
+                    "Usage of <b>SQLite</b> detected. It should only be used for dev/testing. "
+                    "Do not use <b>SQLite</b> as metadata DB in production. "
+                    "We recommend using Postgres or MySQL. "
+                    f"<a href='{db_doc_page}'><b>Click here</b></a> for more information."
+                ),
+                category="warning",
+            )
+
+        if not unit_test_mode and conf.get("core", "executor") == "SequentialExecutor":
+            exec_doc_page = get_docs_url("executor/index.html")
+            flash(
+                Markup(
+                    "Usage of <b>SequentialExecutor</b> detected. "
+                    "Do not use <b>SequentialExecutor</b> in production. "
+                    f"<a href='{exec_doc_page}'><b>Click here</b></a> for more information."
+                ),
+                category="warning",
+            )
         hide_paused_dags_by_default = conf.getboolean('webserver', 'hide_paused_dags_by_default')
 
         default_dag_run = conf.getint('webserver', 'default_dag_run_display_number')