AWS Cost Audit: 7 Things We Found Wasting Money Every Month

AWS Cost Audit: 7 Things We Found Wasting Money Every Month#

After our AWS bill crossed $18,000/month for a 15-person startup, we did a proper audit. We found $6,200 in monthly waste. Here's every item.

1. Idle Load Balancers ($420/month)#

Three ALBs were still running from decommissioned staging environments. Each costs ~$16/month base plus LCU charges.

Fix: We added a Terraform lifecycle check that tags ALBs with the owning team and a TTL. A weekly Lambda deletes anything past its TTL with zero healthy targets.

2. Oversized RDS Instance ($1,800/month)#

Our production database was on db.r6g.2xlarge. CloudWatch showed average CPU at 12% and memory at 35%.

Fix: Downgraded to db.r6g.large during a maintenance window. Set up a CloudWatch alarm for CPU > 70% so we'll know when to scale back up.

3. Unattached EBS Volumes ($280/month)#

14 EBS volumes were sitting with status "available"—leftovers from terminated EC2 instances.

Fix: Scripted a check:

aws ec2 describe-volumes \
  --filters Name=status,Values=available \
  --query 'Volumes[*].{ID:VolumeId,Size:Size,Created:CreateTime}' \
  --output table

Snapshot anything older than 30 days, then delete.

4. Forgotten Snapshots ($640/month)#

We had 2,400 EBS snapshots going back 3 years. Most were from AMIs we no longer use.

Fix: Implemented AWS Data Lifecycle Manager with a 90-day retention policy.

5. NAT Gateway Data Transfer ($1,400/month)#

Our NAT Gateway was processing 800GB/month. Much of it was S3 traffic from private subnets.

Fix: Added a VPC Gateway Endpoint for S3. Free, and it cut NAT traffic by 60%.

resource "aws_vpc_endpoint" "s3" {
  vpc_id       = aws_vpc.main.id
  service_name = "com.amazonaws.us-east-1.s3"
  route_table_ids = [aws_route_table.private.id]
}

6. Over-Provisioned Lambda Memory ($380/month)#

Every Lambda was set to 1024MB by default. AWS Power Tuning showed most needed 256MB.

Fix: Ran Power Tuning on our top 10 functions and right-sized them.

7. Missing Reserved Instances ($1,280/month)#

We were paying on-demand for 4 EC2 instances that had been running for 2 years.

Fix: Purchased 1-year no-upfront reserved instances for predictable workloads.

Best Practices for Ongoing Cost Control#

• Monthly cost review with a tagged cost allocation report
• Budget alerts at 80% and 100% of expected spend
• Terraform-managed resources so nothing is created outside of code
• Quarterly audit of unused resources using AWS Trusted Advisor

The $6,200/month we saved required about 8 hours of work. That's an annualized return of $74,400 for one day of effort.