AWS

Data transfer out

First 100GB/month is free, then $0.09/GB. A site serving 1TB/month of assets pays ~$81/month just in egress. CloudFront reduces this but adds its own per-request fees. Cross-region transfer is $0.02/GB, multi-region architectures multiply this cost.

NAT Gateway tax

Each NAT Gateway costs $0.045/hour ($32.40/month) plus $0.045/GB processed. A VPC with 2 AZs running NAT Gateways costs $65/month before any traffic. This catches every team running private subnets, which is the AWS-recommended security practice.

Cross-AZ data transfer

$0.01/GB in each direction between availability zones. Multi-AZ RDS, ECS tasks spread across AZs, and ALB routing all generate cross-AZ traffic. A busy microservices architecture can rack up $50-200/month in cross-AZ fees alone.

RDS Multi-AZ doubles the price

A db.m5.large PostgreSQL instance costs $0.192/hour ($138/month) in Single-AZ. Enable Multi-AZ for production reliability and it doubles to ~$276/month. Multi-AZ is near-mandatory for production but rarely included in initial cost estimates.

EBS storage is not cheap at scale

gp3 volumes cost $0.08/GB/month. A 500GB database volume costs $40/month. But IOPS above 3,000 and throughput above 125 MB/s cost extra. Provisioned IOPS (io2) at $0.065/IOPS/month can add hundreds of dollars for database workloads.

CloudWatch logging costs

Log ingestion costs $0.50/GB. A busy application generating 50GB/month of logs pays $25/month just for ingestion, plus $0.03/GB/month for storage. Most teams do not budget for this until the bill arrives.

Elastic IP charges

As of February 2024, AWS charges $0.005/hour ($3.60/month) for every public IPv4 address, including those attached to running instances. A setup with 10 public IPs costs $36/month for addresses alone.

Support plan costs

Basic support is free but only covers billing. Developer support starts at $29/month or 3% of monthly spend. Business support (recommended for production) is $100/month or 10% of spend up to $10K then lower tiers. A $5,000/month AWS bill means $500/month in Business support.

Free tier expiration trap

EC2 (750hrs t3.micro), RDS (750hrs db.t3.micro), and S3 (5GB) free tiers expire after 12 months. Many startups budget assuming free tier and get surprised by a 3-10x cost jump at month 13. Lambda and DynamoDB free tiers are permanent.

Reserved Instance commitment risk

1-year or 3-year Reserved Instances save 30-60% but require upfront commitment. Over-provisioning RIs for workloads that shrink or migrate wastes the entire commitment. No cancellation or refund, you can sell unused RIs on the marketplace but at a discount.