existing solution to build a bitcoin address-balance index

Question

I've a full node running in a AWS vm. I want to develop an app which would be able to provide balance for a given btc address. I know blockchain.info and blockexplorer.com exists but I want to do my own but a simple one, just to do the balance query. I want to support a high request bandwidth and each request to work in O(1) complexity. Towards that goal, I'm thinking if

1. I can extract out all the unique btc addresses from blockchain
2. run a script which takes btc address and runs "bitcoin-cli getbalance" from my node to obtain balance for that address
3. Build a in-memory cache of address->balance or in mongodb, then I can do it. Does this plan look good? Is there a better alternative? Are there existing open-source solutions that I can use to do this all, saving me lot of development work? How do I go about each step? Once the infra is set, it should be easy to keep it uptodate since blocks are added every 10mins. I think a event based system can be setup to trigger when blocks added. But setting up the infra is the problem here.

Please help. Much appreciated.