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Fly.io

Fly.io works well for Flet apps: it supports WebSockets, deploys close to users via multiple regions, and has a free tier suitable for small projects.

Prerequisites​

  1. Install flyctl.
  2. Authenticate:
fly auth login

Project files​

Place the following files in your app directory.

requirements.txt​

At minimum:

requirements.txt
flet

fly.toml​

Fly app configuration:

fly.toml
app = "<your-app-name>"

kill_signal = "SIGINT"
kill_timeout = 5
processes = []

[env]
  FLET_SESSION_TIMEOUT = "60"

[http_service]
  internal_port = 8000
  force_https = true
  auto_stop_machines = true
  auto_start_machines = true
  min_machines_running = 0

  [http_service.concurrency]
    type = "connections"
    soft_limit = 200
    hard_limit = 250
  • Replace <your-app-name> with the app name you want. It will also be used in the final URL of your app, in the form, https://<your-app-name>.fly.dev.
  • internal_port must correspond to the FLET_SERVER_PORT, which is 8000 by default.
  • FLET_SESSION_TIMEOUT controls session lifetime (seconds).
  • For other variables, see environment variables reference.

Dockerfile​

Create a Dockerfile containing the commands to build your application container, for example:

Dockerfile
FROM python:3-alpine

WORKDIR /app

COPY requirements.txt ./
RUN pip install --no-cache-dir -r requirements.txt

COPY . .

EXPOSE 8000

CMD ["python", "main.py"]

main.py is the app's entry point. If your file name differs, update accordingly.

Info

Fly.io deploys apps as Docker containers and provides a free remote Docker builder, so you don’t need Docker installed locally.

Deploy​

From your app directory:

  1. Create the Fly app:

    fly apps create --name <your-app-name>

  2. Deploy:

    fly deploy

  3. Open app in browser:

    fly apps open