If you have multiple web servers in your cluster, make sure to use a shared storage location like Amazon S3, DigitalOcean Spaces, or some other location. This way your files will always be accessible when they are requested. If you stored them on disk, your file might be saved to one web server, but the load balancer might send the request for the file to another web server, resulting in a 404. That's why you'll need a shared storage location as you scale up.