# Lambda, Web Functions or Workers?

> Where should this piece of logic run? Classic Lambda for events and heavy compute. Lambda Web Functions for HTTP business logic, once in your region. Workers at the edge, for waiting, spikes and real-time.

- A decision guide from The Stack by Nicolas Dao (Cloudless Labs, Sydney)
- Web page: https://cloudlesslabs.com/stack/guides/compute-choice/. The whole stack in one file: https://cloudlesslabs.com/stack/brief.md
- Tools: [AWS Lambda](https://cloudlesslabs.com/stack/aws-lambda/index.md) (My default), [Lambda Web Functions](https://cloudlesslabs.com/stack/aws-lambda-web-functions/index.md) (Watching), [Cloudflare Workers](https://cloudlesslabs.com/stack/cloudflare-workers/index.md) (My default)

## The short version

| If the logic… | Run it on |
|---|---|
| reacts to SQS, S3, EventBridge, Cognito or a schedule | **Classic Lambda** |
| needs heavy CPU, lots of memory, native modules or another language | **Classic Lambda** |
| is an HTTP API or web app that mostly waits on Postgres | **Lambda Web Functions** (once in your region), otherwise classic Lambda |
| sits in front of your backend: auth, rate limits, webhooks, streaming, spikes | **Workers** |
| needs WebSockets or live shared state | **Workers + Durable Objects** |

## Move from Lambda to Web Functions when

- HTTP APIs behind function URLs mostly wait on Postgres: merge them into one Express or Hono app.
- Aurora connections run out: one environment shares one pool across up to 128 requests.
- Requests are slow. At 2,000 requests a second:

| Time per request | In flight | Web Functions | Classic Lambda |
|---|---|---|---|
| 100 ms | 200 | ~4 environments | 200 instances, fine |
| 500 ms | 1,000 | ~16 environments | At the 1,000 default |
| 1 s | 2,000 | ~32 environments | Throttled unless the quota is raised |
| 20 s (LLM stream) | 40,000 | ~313 environments | Far over the default |

## Move a Worker to Web Functions when

- It grew into business logic that needs native modules, more than 128 MB or full Node.js.
- It calls AWS with stored keys: Web Functions get an IAM role.
- It needs a private VPC database, or compliance needs everything on the AWS bill.

## Where Web Functions lose to Workers

WebSockets (not supported), spikes from zero (10,000 req/s per endpoint by default, and new environments must start), rarely-hit webhooks (scale to zero means a cold first request), global users (5 regions vs every Cloudflare location), huge bodies, and deliverables that must run for years without runtime upgrades.

## Price comparison (USD a month, before free tiers)

| Scenario | Classic Lambda | Web Functions | Workers |
|---|---|---|---|
| REST API: 10M requests, 100 ms, 10 ms CPU | $8.67 | ~$8.72 | $6.40 |
| Same API at 1B requests | ~$867 | ~$600 | ~$501 |
| LLM streaming proxy: 1M chats × 20 s | $33.50–167 | ~$3.40 | ~$0 extra |
| Server-rendered app: 5M page views | $11 | ~$12 | ~$8.40 |
| PDF rendering: 100k × 8 s CPU | ~$21 | ~$22, blocks other requests | Not possible |
| Webhook hit 3× a month | ~$0 | ~$0 | ~$0 |
| Live auction (WebSockets) | ~$407 via API Gateway | Not supported | $15–30 with Durable Objects |

Rates: Lambda Arm $0.0000133334/GB-s and $0.20/M requests. Web Functions (Sydney price list, not launched) $0.0000279955/vCPU-s, $0.0000037065/GB-s, $0.30/M requests, assuming 300–500 MB in use and environments up all month. Workers $5 base including 10M requests and 30M CPU-ms, then $0.30/M and $0.02/M CPU-ms.

**What the numbers say:** for typical APIs, Web Functions cost about the same as Lambda; you migrate for the connection pool and the simpler app. At high volume they're about 30% cheaper. For long waits they're as cheap as Workers.

## Related

- [An API for my app](https://cloudlesslabs.com/stack/use-cases/api.md): the use case this guide works through
- [AWS Lambda](https://cloudlesslabs.com/stack/aws-lambda/index.md): the full entry (verdict, pricing, gotchas)
- [Lambda Web Functions](https://cloudlesslabs.com/stack/aws-lambda-web-functions/index.md): the full entry (verdict, pricing, gotchas)
- [Cloudflare Workers](https://cloudlesslabs.com/stack/cloudflare-workers/index.md): the full entry (verdict, pricing, gotchas)
- [Every decision guide](https://cloudlesslabs.com/stack/brief.md): listed at the end of the brief
- [Map of every Markdown file on cloudlesslabs.com, with what each one answers](https://ask.cloudlesslabs.com)