Dockerize web-based Flet Application

[pangoro24]

I am not a really expert on docker but following the https://flet.dev/docs/guides/python/deploying-web-app/fly-io, I wanted to try my demo in my own computer. When I run the app from my local virtual env, the web app is displayed without problem. However, when I try to run it from a docker container, even when the container is running without issues, it give me error: (failed)net::ERR_EMPTY_RESPONSE

Docker commands used to create the image and run the container
docker build --tag flet-app:latest .
docker run -it -p 62590:62590 -p 8080:8080 flet-app

Source Code

import flet as ft

def main(page: ft.Page):
    page.add(ft.Text(value="Hello world from containerized Flet app!"))

ft.app(target=main, view=ft.WEB_BROWSER)

dockerfile

# syntax=docker/dockerfile:1

FROM python:3.8-slim-buster

WORKDIR /app

COPY requirements.txt requirements.txt
RUN pip3 install -r requirements.txt

COPY . . 

EXPOSE 8080 62590

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

[FeodorFitsner]

Try this Dockerfile which works great for Fly.io environment. Let me know if that worked.

[arminus]

I think the key here is that you start your app with

ft.app(target=main, port=8080, view=ft.WEB_BROWSER)

Then you don't need to expose 62590 - which is pointless anyway, because unless you specify the port for ft.app(...) explicitly, fletd starts on a random port which your Docker will never know about.

At any rate, this way, my brief test worked.

[pangoro24]

Thanks for your comments. It helped to fix my dockerfile.

FROM python:3-alpine

# Set the working directory to /app
WORKDIR /app

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

COPY ./app ./app

EXPOSE 8080

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

and compose file is:

version: '3.8'
services:
  webapp: 
    build: .
    ports:
      - '8080:8080'
    restart: always
    container_name: fletappcontainer
    image: webapp/fletapp:latest

Just as a reference for the community, I leave the demo in a public github repo. https://github.com/pangoro24/pyflet
and image on DockerHub: https://hub.docker.com/repository/docker/pangoro24/flet-python

[FeodorFitsner]

It's great you got it working and thanks for sharing the resulting files! We will include that into the guide.

Btw, it's also possible to define Flet port in Dockerfile via FLET_SERVER_PORT environment variable:

ENV FLET_SERVER_PORT=8080

and have flet.app() call as:

ft.app(target=main, view=None)

[pangoro24]

thank you @FeodorFitsner for your feedback. I updated the repo and plus, added an env file to set the PORT

[Shahin-rmz]

Try this Dockerfile which works great for Fly.io environment.

It's very nice.
thanks.
Can we have an official docker compose file for Flet?
I'm going to deploy Flet on a selfhosted server.

[shinriyo]

git clone https://github.com/flet-dev/examples
cd examples/python/apps/icons-browser
docker build --tag flet-app:latest .
docker run -it -p 62590:62590 -p 8080:8080 flet-app

but I can't access both of them.

http://localhost:8080/
http://localhost:62590/

[Spritaro]

It appears that Flet switches to the browser when running inside a container. But it fails to call open_in_browser() function if view option is not set to WEB_BROWSER.

flet/sdk/python/packages/flet/src/flet/flet.py

Lines 147 to 167 in 2150cc5

	if (
	(view == FLET_APP or view == FLET_APP_HIDDEN)
	and not is_linux_server()
	and url_prefix is None
	):
	fvp, pid_file = open_flet_view(
	conn.page_url, assets_dir, view == FLET_APP_HIDDEN
	)
	try:
	fvp.wait()
	except (Exception) as e:
	pass
	else:
	if view == WEB_BROWSER and url_prefix is None:
	open_in_browser(conn.page_url)
	try:
	while True:
	if terminate.wait(1):
	break
	except KeyboardInterrupt:
	pass

It would be nice if it could raise an error or a warning though.

[FeodorFitsner]

@Spritaro so, we should add another check for running inside Docker container before opening web browser, right?

[Spritaro]

Thank you @FeodorFitsner for your response. Yes, adding another check before opening or an else block afterwards will be helpful.

[FeodorFitsner]

Sorry, I just realized you need to pass view=None when running in container:

ft.app(main, port=8080, view=None)