The line item nobody budgets for:
"Data Transfer — Inter-Region Out"
Last audit: ₹4,20,000/month. The founder had no idea.
It wasn't a bug. It was replication jobs firing from ap-south-1 to ap-southeast-1 that ran nightly since 2023. Set up for one use case. Never turned off.
The pattern is almost always:
→ A DR replication from Mumbai to Singapore (or to us-east-1)
→ A Kinesis stream fan-out across AZs
→ A Datadog exporter pushing logs to a US tenant
→ A CloudWatch log subscription that cross-accounts
→ A NAT Gateway fee where a VPC endpoint would have cost zero
Each one is pennies per GB. At TB-per-month scale, pennies become lakhs.
The reason nobody catches it: AWS groups these under generic "Data Transfer" in the bill. Cost Explorer doesn't highlight inter-region traffic by default.
The fix isn't one CLI query. It's:
→ Enable CUR with Resource IDs. Look at TransferOut lines by region pair.
→ Replace public S3/DynamoDB calls with VPC endpoints (free for gateway endpoints)
→ Replicate only what your DR plan actually tests, not what's documented
→ For logs/metrics: aggregate in-region before forwarding out
One company in our audit cut this line item by 73% in 30 days. Zero functional change.
If you've never audited your egress line, you're probably paying for a 2023 decision you forgot about.
Repost. Your CFO will thank you.
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