When reviewing your AWS bill, you might encounter this line item:

$0.010 per GB - regional data transfer - in/out/between EC2 Avail Zones 
or when using public/elastic IP addresses or ELB

Even with a single micro instance running, several scenarios can trigger these data transfer fees:

• Communication between EC2 instances in different Availability Zones
• Data transferred through Elastic Load Balancers (ELB)
• Traffic using public or Elastic IP addresses
• Some monitoring and management traffic from AWS services

Consider these common cases where you might see small charges:

# Example 1: Simple web request
curl http://your-ec2-instance/public-endpoint

# Example 2: Database replication across AZs
# (Even if you didn't explicitly configure this, some AWS services might do it)
aws rds create-db-instance \
    --db-instance-identifier mydb \
    --availability-zone us-east-1a \
    --db-instance-class db.t2.micro \
    --engine mysql

Use AWS Cost Explorer with these filters:

{
  "Dimensions": {
    "Key": "SERVICE",
    "Values": ["AWS Data Transfer"]
  },
  "Tags": {
    "Key": "CostCenter",
    "Values": ["Production"]
  }
}

To minimize costs:

• Keep instances in the same AZ when possible
• Use private IPs for inter-instance communication
• Consider VPC endpoints for AWS services

Run these AWS CLI commands to investigate:

# Check data transfer metrics
aws cloudwatch get-metric-statistics \
    --namespace AWS/EC2 \
    --metric-name NetworkOut \
    --dimensions Name=InstanceId,Value=i-1234567890abcdef0 \
    --start-time 2023-01-01T00:00:00Z \
    --end-time 2023-01-31T23:59:59Z \
    --period 86400 \
    --statistics Sum

# List all elastic IPs associated with your account
aws ec2 describe-addresses

When you see a line item for "$0.010 per GB - regional data transfer" on your AWS bill, it typically refers to traffic between EC2 instances in different Availability Zones (AZs) within the same region, or when using public/elastic IPs and ELBs. Even with just one micro instance running, you might still incur these charges.

Here are common scenarios that trigger these charges:

• Your instance communicates with other AWS services in different AZs
• You use Elastic Load Balancing (ELB) which distributes traffic across AZs
• Your application makes calls to public AWS endpoints (S3, SQS, etc.)
• System monitoring or logging services transfer data between AZs

Even a simple CloudWatch monitoring setup can generate inter-AZ traffic:

# Example CloudWatch Agent configuration (generates metrics traffic)
{
  "metrics": {
    "append_dimensions": {
      "InstanceId": "${aws:InstanceId}"
    },
    "metrics_collected": {
      "cpu": {
        "measurement": ["cpu_usage_idle"],
        "resources": ["*"],
        "metrics_collection_interval": 60
      }
    }
  }
}

Use AWS Cost Explorer with these filters:

1. Service: EC2
2. Operation: DataTransfer-Regional-Bytes
3. Usage Type: DataTransfer-Regional-Bytes

Implementation tips to minimize costs:

• Use VPC endpoints for AWS services
• Configure security groups to restrict unnecessary outbound traffic
• Monitor your instance's network interfaces with:

# Check network usage on Linux instances
vnstat -i eth0
# Or for Windows:
Get-NetAdapterStatistics | Select-Object Name,ReceivedBytes,SentBytes

These are typical scenarios where you'll see the charge:

The small charges you're seeing are likely from system processes or minor traffic bursts. AWS bills these in increments, so even a few MB of monitoring data can appear on your bill.