Deploy FastAPI serverlessly.

Why FastAPI fits Phemeral

No adapters, no wrappers, no config.

• No need for config files

  Phemeral figures out how your FastAPI app is structured, what dependencies you're using, what version of Python you're using, and builds your app without the need for config files.

• Runs serverlessly without compromises

  Websockets and SSE are supported. And even though your app is running on serverless infra, it runs with uvicorn just like normal. So, no more adapters to get your app running for serverless (Mangum).

• Free concurrency even if you didn't write async

  Since each request is handled in an ephemeral serverless environment, concurrent requests won't block each other. Even if your app isn't using asyncio.

• Lightning fast cold starts.

  When scaling up, your app goes from dead to alive in less than 50 ms. Pretty darn fast.

Deployment model

Github integration gives you CI/CD. New deployments are triggered on pushes to your repo.

1. 01

   Push

   A push triggers a deployment.

2. 02

   Detect

   Python version, framework, package manager, project root and entry point are detected from source.

3. 03

   Build

   Dependencies are installed, the project is built.

4. 04

   Live

   The deployment is assigned a URL and any custom domains you've set up will route to the latest deployment.

Platform features you need for a FastAPI app

• Environments

  Production, Staging, and Development are created with every project. Make as many other environments as you need too.

• Environment variables

  Manage your environment variables for your app. Set env vars for each of your environments.

• Custom domains

  Use your custom domains for your hosted apps.

• Build and runtime logs

  Observability you need. Monitor build logs as your deployment is built, and runtime logs as it runs. Catch bugs before they're bugs.

• Custom start command

  Set a custom start command if you're doing something fancy.

• CRON jobs

  Set up CRON jobs to make requests to your deployment on whatever schedule you want.

Everything around the app

Databases, static files, background work and scaling.

Databases

Provision managed serverless Postgres clusters inside the project.

Our managed serverless Postgres scales up and down to match your traffic

Static files

Serve assets from the app itself by mounting StaticFiles in FastAPI.

app.mount("/static", StaticFiles(directory="static"))

Background work

Scheduled webhooks cover recurring jobs: cache warming, maintenance endpoints, and application-level tasks triggered on a schedule.

0 0 3 * * * → every day at 03:00 UTC

Scaling and connections

Deployments scale to zero when idle and up on demand.

A minimal FastAPI project

That's all you need. No config files to be found.

my-project/
├── .python-version
├── pyproject.toml
├── uv.lock
└── app/
    └── main.py

from fastapi import FastAPI

app = FastAPI()

@app.get("/")
def read_root():
    return {"message": "Hello, World!"}

• Deploy Your First ProjectProject, repository, branch mapping, first push.
• Project Structure RequirementsProject root, dependency priority, entry point.
• Supported FrameworksServers, protocols and package managers.
• WebSockets & SSEReal-time connections, keepalives, billing.
• Managed PostgresCreate a cluster and connect your app.
• Set a Custom Start CommandOverride the autodetected command.

FastAPI on Phemeral, answered