AWS Lambda

Duration billing rounds up to the nearest millisecond, but memory billing is per-GB-second at allocated memory (not used memory). Allocating 1 GB but using 200 MB still bills for 1 GB, right-sizing memory is critical

Provisioned Concurrency

eliminates cold starts but charges $0.0000041667/GB-second even when idle. Provisioning 100 instances at 512 MB costs ~$54/month whether they handle traffic or not

Data transfer out

Lambda itself is cheap, but responses that cross AZ boundaries or leave AWS incur standard EC2 data transfer charges ($0.01-0.09/GB). High-traffic APIs serving large payloads can have transfer costs exceed compute costs

VPC-attached Lambda

connecting to RDS or ElastiCache inside a VPC adds ~200-500ms cold start overhead and creates ENI resources. VPC Lambda also requires NAT Gateway ($32/month + $0.045/GB) for outbound internet access

Ephemeral storage

default 512 MB included, up to 10 GB available at $0.0000000309/GB-second. Processing large files (video, ML models) can add meaningful storage costs

CloudWatch Logs

every Lambda invocation generates logs. At 5M invocations/month generating 1 KB each, log ingestion costs $2.50/month. High-verbosity logging on high-traffic functions can cost more than the compute itself

API Gateway costs are separate

if fronting Lambda with API Gateway, add $3.50/million requests (REST API) or $1.00/million (HTTP API). For some workloads, the gateway costs more than Lambda

Step Functions orchestration

coordinating multiple Lambda functions via Step Functions costs $25 per million state transitions, a 10-step workflow processing 1M executions/month costs $250/month in orchestration alone