Unexpected billing

Hello.

What database engine are you using with RDS?
If you are using version 2 of Aurora MySQL, extended support fees will be added from December 2024, so RDS prices may have increased.
https://docs.aws.amazon.com/AmazonRDS/latest/AuroraUserGuide/extended-support.html

This paid offering gives you more time to upgrade to a supported major engine version. For example, the Aurora end of standard support date for Aurora MySQL version 2 is October 31, 2024. However, you aren't ready to manually upgrade to Aurora MySQL version 3 before that date. In this case, Amazon Aurora automatically enrolls your cluster in RDS Extended Support on October 31, 2024, and you can continue to run Aurora MySQL version 2. Starting December 1, 2024, Amazon Aurora automatically charges you for RDS Extended Support.

I understand your concern about the unexpected increase in your AWS bill, particularly the significant jump in your relational database costs. Here are some steps you can take to address this issue:

1. Review your AWS Cost Explorer: This tool can help you break down and analyze your costs in detail. Look for any unusual spikes or changes in usage patterns for your relational database service.

2. Check for changes in your database usage: Consider if there were any changes in your application or workload that might have increased database usage, such as increased traffic, new features, or data processing jobs.

3. Verify your instance type and pricing: Ensure that there haven't been any unintended changes to your database instance type or pricing model. Sometimes, small changes can lead to significant cost increases.

4. Look for any new or modified resources: Check if any new resources were added or existing ones modified that might be interacting with your database and increasing its usage.

5. Contact AWS Support: If you can't identify the reason for the cost increase or if you believe there's an error, it's advisable to open a case with AWS Support under the "Account and billing" category. They have the tools and visibility to investigate your specific billing situation and can provide more detailed insights.

6. Set up billing alerts: To avoid future surprises, consider setting up AWS Budgets or CloudWatch alarms to notify you when your costs exceed certain thresholds.

Remember, AWS billing is based on actual usage, so it's important to regularly monitor your resources and optimize them for cost-efficiency. If you find that the increased costs are due to legitimate increased usage, you might want to explore options for optimizing your database performance or consider using reserved instances for long-term cost savings.
Sources
Unusually high AWS monthly bill due to Directory Services | AWS re:Post
unexpected billing | AWS re:Post