# app.py
from flask import Flask

app = Flask(__name__)

@app.route("/")
def flag():
    return "<p>flag{that_was_easy!}</p>"

FROM python:3
RUN pip install flask
COPY app.py .
EXPOSE 5000
CMD flask run --host=0.0.0.0

First we create a simple challenge that just emits our flag on connect.

It must include a Dockerfile which attempts to EXPOSE a port.

Finally you should be able to build your docker image with docker build -t project .

Next we create a new service inside of CTFd

Finally we push up our image to CTFd which will automatically handle the rest.

docker login registry.ctfd.io
docker tag <image> registry.ctfd.io/demo/project
docker push registry.ctfd.io/demo/project

The challenge will go from push to building to deployed until finally your challenge will automatically be given a port and deployed.

Need an unencrypted TCP port for netcat? Read about Requesting a TCP Port!