AWS Lambda vs ECS Fargate vs EC2 — Which Compute for UK Software? (2025)
AWS Lambda is the right default for most UK API workloads: zero infrastructure management, automatic scaling, pay-per-request, and Cyber Essentials OS patching handled by AWS. ECS Fargate is right for containerised workloads needing more control (longer execution, stateful background processing, consistent warm instances). EC2 should only be used when you have specific requirements that Lambda and ECS cannot satisfy — sustained compute-intensive workloads at scale. Compute choice is the most consequential AWS architecture decision. Here is a UK-focused comparison that includes UK GDPR data residency, Cyber Essentials patching obligations, and FCA operational resilience implications.
| Factor | Lambda | ECS Fargate | EC2 |
|---|---|---|---|
| Cyber Essentials OS patching | ✅ AWS manages OS — no obligation | ✅ AWS manages Fargate runtime — no obligation | ❌ Your responsibility — 14-day requirement |
| UK GDPR data residency | ✅ eu-west-2 — UK London | ✅ eu-west-2 — UK London | ✅ eu-west-2 — UK London |
| Cold start latency | ⚠️ 50–500ms (provisioned concurrency mitigates) | None — always warm containers | None — always running |
| Max execution time | 15 minutes | Unlimited | Unlimited |
| Auto-scaling | ✅ Instant — per invocation | ✅ ECS Service Auto Scaling (seconds) | ASG — minutes to scale |
| Cost (low traffic) | ✅ Near-zero — pay per request | ~£30–50/month minimum | ~£20–150/month minimum (instance type) |
| Cost (sustained high throughput) | Can exceed ECS/EC2 at very high volume | Better TCO | Best TCO at consistent high load |
| FCA PS21/3 — guaranteed compute | ⚠️ Concurrency limits require planning | ✅ Defined task count per service | ✅ Fixed instance count |
| ClickMasters default | APIs, event handlers, background jobs | Long-running services, batch, websockets | Only for specific persistent compute needs |
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