Deploy with a Custom Dockerfile

Any repository can include its own Dockerfile at the root, and if present, it's always used instead of auto-generation — regardless of tech stack. For Python, Go, Ruby, Rust, or anything else that isn't Node.js, this is required, not optional; see Framework Auto-Detection for why.

Requirements

• EXPOSE and actually listen on the port configured in project settings (0.0.0.0:$PORT, not localhost/127.0.0.1 — the health check and reverse proxy connect from outside the container).
• Read configuration from environment variables — DATABASE_URL, PORT, and anything you set yourself are all injected as container env vars, see Environment Variables.
• Respond to at least one HTTP request within the deploy's health-check window, or the deploy is marked failed and traffic stays on the previous version.

Example — Python (Flask/Gunicorn)

FROM python:3.12-slim
WORKDIR /app
COPY requirements.txt .
RUN pip install --no-cache-dir -r requirements.txt
COPY . .
EXPOSE 8000
CMD ["gunicorn", "-b", "0.0.0.0:8000", "app:app"]

Example — Go

FROM golang:1.22 AS builder
WORKDIR /app
COPY . .
RUN CGO_ENABLED=0 go build -o server .

FROM alpine:3.20
COPY --from=builder /app/server /server
EXPOSE 8000
CMD ["/server"]

Related documentation