Do not run initialization code concurrently

backend/app.py

@@ -3,6 +3,7 @@ from flask_cors import CORS
 from flask_jwt_extended import JWTManager
 import flask_migrate
 from jsonschema.exceptions import ValidationError
+from NamedAtomicLock import NamedAtomicLock
 from werkzeug.exceptions import BadRequest
 
 # These imports are required
@@ -68,27 +69,36 @@ app.logger.info("Starting dashboard backend.")
 cors = CORS(app)
 
 db.init_app(app)
-with app.app_context():
-    # We have reset the alembic migration history at Stackspin version 2.2.
-    # This checks whether we need to prepare the database to follow that
-    # change.
-    migration_reset.reset()
-flask_migrate.Migrate(app, db)
-try:
-    with app.app_context():
-        flask_migrate.upgrade()
-except Exception as e:
-    app.logger.info(f"upgrade failed: {type(e)}: {e}")
-    sys.exit(2)
-
-# We need this app context in order to talk the database, which is managed by
-# flask-sqlalchemy, which assumes a flask app context.
-with app.app_context():
-    # Load the list of apps from a configmap and store any missing ones in the
-    # database.
-    cluster_config.populate_apps()
-    # Same for the list of oauthclients.
-    cluster_config.populate_oauthclients()
+
+# We'll now perform some initialization routines. Because these have to be done
+# once at startup, not for every gunicorn worker, we take a machine-wide lock
+# for this.
+init_lock = NamedAtomicLock('dashboard_init')
+if init_lock.acquire():
+    try:
+        with app.app_context():
+            # We have reset the alembic migration history at Stackspin version 2.2.
+            # This checks whether we need to prepare the database to follow that
+            # change.
+            migration_reset.reset()
+        flask_migrate.Migrate(app, db)
+        try:
+            with app.app_context():
+                flask_migrate.upgrade()
+        except Exception as e:
+            app.logger.info(f"upgrade failed: {type(e)}: {e}")
+            sys.exit(2)
+
+        # We need this app context in order to talk the database, which is managed by
+        # flask-sqlalchemy, which assumes a flask app context.
+        with app.app_context():
+            # Load the list of apps from a configmap and store any missing ones in the
+            # database.
+            cluster_config.populate_apps()
+            # Same for the list of oauthclients.
+            cluster_config.populate_oauthclients()
+    finally:
+        init_lock.release()
 
 app.register_blueprint(api_v1)
 app.register_blueprint(web)

backend/requirements.txt

@@ -19,6 +19,7 @@ jinja2-base64-filters==0.1.4
 kubernetes==24.2.0
 MarkupSafe==2.1.1
 mypy-extensions==0.4.3
+NamedAtomicLock==1.1.3
 oauthlib==3.2.0
 pathspec==0.9.0
 platformdirs==2.5.1