What’s the easiest way to stop an EC2 instance from running up charges when I’m not using it?

To prevent an EC2 instance from incurring charges when you're not using it, you have a few options:

1. Stop the instance: You can stop your EC2 instance through the AWS Management Console by:

• Going to the EC2 dashboard
• Selecting your instance
• Choosing "Instance state" > "Stop instance"
• Confirming when prompted

Stopping an instance will halt the compute charges, but be aware that you'll still be billed for associated EBS volumes while the instance is stopped.

2. Terminate the instance: If you no longer need the instance at all, terminating it is the most effective way to prevent all charges. This permanently deletes the instance and its associated EBS volumes (unless you've configured them to persist).

3. Set up monitoring and alerts: AWS doesn't offer an automatic way to pause services when approaching Free Tier limits, but you can:

• Set up AWS Budgets or Free Tier usage alerts
• Create CloudWatch alarms to monitor your EC2 usage
• Configure budget alerts to notify you when approaching a certain spending threshold

4. Check all regions: Make sure to check for instances in all AWS regions to ensure you haven't left any running elsewhere.

5. Remove unused resources: Delete any unnecessary EBS volumes, snapshots, or Elastic IP addresses not associated with running instances, as these can also generate charges.

For your t2.micro instance, if you're using the Free Tier, you get 750 hours per month, but you should still stop or terminate it when not in use to avoid exceeding this limit.
Sources
How to make sure instances on my account terminate to prevent future charges | AWS re:Post
Free tier Ec2, how to avoid overages | AWS re:Post
Use StopInstances with an AWS SDK or CLI - Amazon Elastic Compute Cloud