Unintended EC2 costs.

Unintended EC2 costs can occur for a variety of reasons. It's important to be aware of potential pitfalls to avoid unexpected charges on your AWS bill. Here are some common scenarios that can lead to unintended EC2 costs:

1. Running Instances: Instances that are left running when they are no longer needed can accumulate charges. Always terminate instances that are no longer in use.
2. Elastic IP Addresses: If you allocate an Elastic IP address to your instance and don't release it when the instance is terminated, you will be charged for the unused IP address.
3. EBS Volumes: Even if an EC2 instance is terminated, the associated EBS (Elastic Block Store) volumes might still be incurring charges if they were not deleted. Unused EBS volumes, including snapshots, can add up over time.
4. Data Transfer Costs: Data transfer out of AWS can incur charges. Make sure you are aware of any data transfer activities, especially if you have services communicating with resources outside of AWS.
5. Reserved Instances: If you have purchased Reserved Instances, you will be charged for them regardless of whether or not you use the associated instances.
6. Load Balancers: If you have Elastic Load Balancers (ELB) or Application Load Balancers (ALB) associated with your instances, they may continue to incur charges even if the instances they were originally associated with have been terminated.
7. Unused Security Groups and Key Pairs: Security groups and key pairs, if not cleaned up, don't incur direct charges, but they can lead to confusion and mismanagement of resources.
8. Auto Scaling Groups: If you have an Auto Scaling group set up and instances are launched automatically but not terminated when they are no longer needed, this can lead to unnecessary charges.
9. Backup and Snapshot Costs: Regularly review and manage your backups and snapshots. Unused or outdated backups can accumulate costs.
10. Resource Tagging: Properly tagging your resources can help you identify and manage them more effectively, reducing the risk of leaving resources running unintentionally.

To mitigate these risks:

• Use AWS Budgets and Cost Explorer to set up alerts for potential cost overruns.
• Regularly review and audit your AWS resources.
• Utilize AWS Trusted Advisor to get personalized recommendations for optimizing your resources and reducing costs.

By staying vigilant and proactively managing your AWS resources, you can minimize the risk of incurring unintended EC2 costs.