How can I manage costs effectively for my AWS web app?

Just a heads up, make sure to factor in costs from CloudWatch logs, as they can add up quickly. Plus, don't forget about network costs for things like outgoing traffic and inter-availability zone transfers. It's actually tough to cap your spending on AWS; these budgeting tools have about a 24-hour delay, meaning you might get an alert a day after a traffic spike has already happened.

If you're really looking to cut costs, consider that for a simple CRUD app, it might be more economical to skip AWS completely. A basic VPS can run you about $10, and if you find your needs growing, you could always upgrade to a dedicated server or even a load-balanced cluster, which might end up being cheaper than you think.

While you can't set a hard cap on AWS spending, you can get pretty close. Use AWS Budgets with alerts, implement CloudWatch alarms for Lambda and API Gateway, and set sensible service limits and throttles. Typically, API Gateway plus authentication is sufficient protection, but if your app is public-facing, consider adding WAF to prevent bots from increasing your usage. I've noticed that unexpected costs often come from not having enough throttles rather than from hackers or malicious activity.

You might want to explore Lambda function URLs to see if they fit your use case. It could help streamline some aspects of your architecture and potentially save on costs.

One solid approach is to set up AWS Budgets to create alerts that will notify you if you get close to your spending threshold. Just keep in mind that while these alerts can warn you, they won't stop services from running, so you'll still need to monitor and possibly disable services yourself if you hit your limit.