There is not a feature for hot reloading the rasa server. Maybe you could create a feature request here and describe how you would want / expect it to work in more detail?
What would be the complete command to activate the subclasses to do the reload?
–auto-reload Enable auto-reloading of modules containing Action subclasses. (default: False)
There are a few possibilities: you can use a Restful endpoint URL or e.g. Amazon S3. As soon as you update the model, the Rasa server will automatically download it. There is also a configuration option about the poll intervall that you can set when you start Rasa, so it will not spam your logs unnecessarily.
If you really want a zero downtime deployment though, you need at least 2 running Rasa servers and a load-balancer in-between, as even with the auto-loading of the model, there will be a short time, until the new model is activated.