Container (ECS/EKS) vs Serverless (Lambda) cost

About this calculator

Lambda or ECS — the volume crossover

Lambda is cheap at low volumes (often free) and expensive at high volumes. Containers are expensive at low volumes (always-on bill) and cheap at high volumes. The break-even depends on request rate, duration, and memory.

The math

GB-seconds per request = memory MB ÷ 1024 × duration ms ÷ 1000
total GB-seconds = requests × GB-seconds per request
Lambda cost = total GB-seconds × $0.0000166667 + requests × $0.0000002

Default scenario: 50M requests/mo × 250ms × 512MB:

GB-seconds: 50M × 0.125 = 6.25M
Lambda cost: 6.25M × $0.0000166667 + 50M × $0.0000002 = $104 + $10 = $114/mo
Container cost (1 small instance): $320/mo
Lambda wins by $206/mo at this volume.

When containers win

Sustained throughput → instance is "fully utilized" anyway
Long-running connections (websockets, gRPC streams)
Latency-sensitive (Lambda cold start adds 100-500ms first call)
High memory (Lambda max 10GB; certain workloads need 32+ GB)
Workloads needing GPU

When Lambda wins

Bursty / unpredictable traffic
Long idle periods
Sub-second functions
Event-driven (S3 → Lambda, SQS → Lambda)
Cost optimization at low scale

The break-even

Default scenario: $320 / per-request cost ($0.00000228) = ~140M requests/mo before Lambda exceeds container cost. Above 140M req/mo: containers cheaper. Below: Lambda cheaper.

What this calc misses

NAT Gateway / VPC costs (both apply differently)
Cold start latency (real Lambda cost in user experience for low-traffic functions)
Reserved instance discounts on containers (-40-60%)
Lambda Provisioned Concurrency (eliminates cold start; costs more)
API Gateway costs ($1.00 per million requests for REST API on top of Lambda)

FAQ

What about Fargate?

Fargate is between Lambda and EC2. Per-second billing for the container's exact CPU/memory. About 30-50% more expensive than EC2 for sustained workloads but no infrastructure management. Best for workloads that don't fit Lambda (long duration, high memory) but where ops simplicity matters.

Don't I need API Gateway with Lambda?

For HTTP APIs: yes. API Gateway adds $1/million requests for REST or $0.90/million for HTTP. Lambda Function URLs are FREE alternative for simple HTTP endpoints — skip API Gateway when you don't need its features (auth, request validation, etc).

What if my Lambda is slow?

Lambda costs scale with duration. A 5000ms function uses 20x more compute than 250ms. If your Lambda is slow due to inefficient code, OPTIMIZE — same revenue at 1/10 cost. If slow due to inherent work (image processing), containers are usually cheaper. Lambda's sweet spot is sub-1-second functions.