How do you run Uvicorn inside a Docker container?

Uvicorn is widely used in containerised deployments. The key considerations are binding to the right host, setting the correct number of workers, and choosing between running Uvicorn directly or via Gunicorn.

# Dockerfile - single-container Uvicorn
FROM python:3.12-slim

WORKDIR /app

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

COPY . .

# Expose the port
EXPOSE 8000

# Run Uvicorn - bind 0.0.0.0 so Docker can forward traffic
CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "8000",
     "--workers", "4", "--loop", "uvloop", "--http", "httptools",
     "--log-level", "info", "--no-access-log"]

# requirements.txt:
# uvicorn[standard]
# fastapi

# docker-compose.yml
services:
  api:
    build: .
    ports:
      - "8000:8000"
    environment:
      - UVICORN_HOST=0.0.0.0
      - UVICORN_PORT=8000
      - UVICORN_WORKERS=4
      - UVICORN_LOG_LEVEL=info
      - WEB_CONCURRENCY=4
    command: uvicorn main:app

# Health check - uvicorn has no built-in health endpoint
# Add one to your application:
# @app.get("/health")
# def health(): return {"status": "ok"}

Key Docker-specific setting: always use --host 0.0.0.0 inside Docker containers. The default 127.0.0.1 binds to the container's loopback interface only, which means Docker's port forwarding cannot reach it - the service will be unreachable from outside the container.

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