After you upgrade a standard instance to a cluster instance in proxy mode, you do not need to modify the application code. This is because proxy nodes can seamlessly handle architecture changes, allowing you to use the cluster architecture in the same way as you use the standard architecture.
If your business requirements outgrow the capabilities of a standard instance, you can migrate the data of the standard instance to a cluster instance that has proxy nodes without having to modify the code. This significantly reduces your costs.
Proxy nodes can balance loads, route commands, manage the traffic to read replicas, cache hotkey data, and support multi-database usage within a cluster instance. For more information, see Features of proxy nodes.