Day 61: Preventing Denial of Wallet Attacks by Removing Features

Today, on Day 61 of my 100 Days of Cloud challenge, I did something unconventional: I intentionally deleted a feature I had spent hours building. When you transition from traditional software development to Cloud Architecture, you quickly learn that every piece of logic you expose to the user has a direct impact on your monthly bill.

I had initially built a "Force Sync" button in my React frontend. This allowed users to instantly fetch their latest banking data through the Plaid API and immediately generate a fresh Generative AI analysis using Amazon Bedrock. From a UX perspective, it felt snappy and responsive. From a FinOps perspective, it was a ticking time bomb.

This architecture created a classic "Denial of Wallet" vulnerability. If a user was anxiously waiting for a pending coffee transaction to appear and mashed the "Force Sync" button twenty times, they would trigger twenty asynchronous AWS Lambda executions and twenty heavy LLM prompts. A single frustrated user could unknowingly rack up my AI billing budget in a matter of minutes. Furthermore, banking APIs do not settle transactions in true real-time anyway, making the button practically useless for instant gratification.

To protect the system, I eliminated the button entirely. My architecture now relies strictly on Amazon EventBridge, which safely triggers asynchronous background syncing via Amazon SQS workers on a controlled schedule.

To ensure the user still gets immediate value when logging into the dashboard without calling the backend, I built a predictive "Velocity Analysis" module. Instead of asking AWS to calculate their spending trajectory and burn rate, I wrote the algorithm in plain JavaScript directly within the React frontend. By shifting this mathematical load to the client's browser, I dramatically improved the dashboard's usefulness without adding a single cent to my AWS invoice.

The biggest lesson today? Offloading computations to the user's browser is the ultimate FinOps hack. In the cloud, client-side compute is free compute. Ensure your architecture relies on controlled background jobs rather than unpredictable user triggers.