I want to install a Pruned Bitcoin node with limited connections. I will be connecting to it with JSON-RPC to interface with my web application. What happens when I want to fetch information about an address that is not in my pruned blockchain on my node? Can someone explain this to me?
The pruned node will always have the full set of UTXOs available. This includes all spendable transaction outputs, also the ones of addresses that you hadn't been watching previously. If you want to look up old transactions of a previously unwatched address, your node will not be able to provide the information if you have already pruned those blocks. You'd either have to redownload and resync the blockchain to look for them, store the full blockchain in the first place, or use a third party service to look up the information.