PYTHONUNBUFFERED=1 helped, but the main problem was not being able to connect to mariadb...

swagger_server/__main__.py

@@ -4,19 +4,13 @@ import connexion
 
 from swagger_server import encoder
 
-print("We in main file")
-
 def main():
-    print("Starting app1")
     app = connexion.App(__name__, specification_dir='./swagger/')
-    print("Starting app2")
     app.app.json_encoder = encoder.JSONEncoder
-    print("Starting app3")
     app.add_api('swagger.yaml', arguments={'title': 'OpenAPI definition'}, pythonic_params=True)
     print("Starting app4")
     app.run(port=8080)
 
 
 if __name__ == '__main__':
-    print("Starting main function")
     main()