Accessing a Vite UI Built in a Docker Container: Resolving ERR_EMPTY_RESPONSE

Problem Overview

If you've built a React UI using Vite and Docker, but encountered an ERR_EMPTY_RESPONSE when trying to access it, you're not alone. This issue can be particularly confusing because running the app locally with npm run dev -- --host 0.0.0.0 works just fine. However, using Docker can sometimes complicate things, resulting in empty responses. Let’s take a closer look at the root cause and how to solve it.

Symptoms:

• Running curl http://localhost:3002/ returns: curl: (52) Empty reply from server.
• Running locally without Docker works, but Dockerizing the frontend results in an inaccessible UI.

Tech Stack Involved:

• Vite
• React
• Docker / Docker-Compose
• (WebSocket, Python, FastAPI)

Docker Compose and Dockerfile Setup

Your Docker Compose file might look something like this:

docker-compose.yml:

services:
  fastapi-backend:
    build:
      context: ./be
      dockerfile: Dockerfile
    restart: always
    volumes:
      - ./fastapi_backend:/app
    ports:
      - "8000:8000"

  react-frontend:
    build:
      context: ./fe
      dockerfile: Dockerfile
    restart: always
    ports:
      - "3002:3002"

And the Dockerfile for the frontend:

Dockerfile:

# Use the official Node.js 18 image
FROM node:18-alpine

# Copy package files to leverage Docker cache
COPY package*.json ./

# Install dependencies
RUN npm install

# Copy the rest of the application
COPY . .

# Expose port 3002
EXPOSE 3002

# Command to start the app with Vite
CMD ["npm", "run", "dev", "--", "--host", "0.0.0.0", "--port", "3002"]

Why is This Happening?

The problem lies in the lack of a specified working directory. When Docker runs commands, it needs to understand from which directory the application should be served. In the absence of a specified directory, the container doesn’t know where to find the necessary files, resulting in an empty response.

Solution

To solve this, you need to define the working directory explicitly using the WORKDIR command in your Dockerfile. By setting the working directory to /app, you ensure that every subsequent command is run from that directory, which makes the application accessible.

Here is the updated Dockerfile:

# Use the official Node.js 18 image
FROM node:18-alpine

# Set the working directory
WORKDIR /app

# Copy package files to leverage Docker cache
COPY package*.json ./

# Install dependencies
RUN npm install

# Copy the rest of the application
COPY . .

# Expose port 3002
EXPOSE 3002

# Command to start the app with Vite
CMD ["npm", "run", "dev", "--", "--host", "0.0.0.0", "--port", "3002"]

Vite Configuration

Additionally, make sure your vite.config.js is configured properly. Here’s an example configuration:

import { defineConfig } from "vite";
import react from "@vitejs/plugin-react";

// https://vitejs.dev/config/
export default defineConfig({
  plugins: [react()],
  server: {
    watch: {
      ignored: [
        "**/vite.config.ts",
        "**/.env",
        "**/node_modules/**",
        "**/dist/**",
      ],
    },
    host: true,
    port: 3002,
    strictPort: true,
  },
});

Explanation

Adding the WORKDIR /app command solves the issue because it tells Docker to:

1. Set /app as the current working directory inside the container.
2. Run commands like npm install and npm run dev from /app.
3. Ensure that Vite can properly serve the UI when accessed via http://localhost:3002/.

Conclusion

If you encounter the ERR_EMPTY_RESPONSE issue when using Docker for your Vite UI project, make sure you have set a working directory in your Dockerfile. With the WORKDIR command in place, your Docker container will know where to look for files, and your Vite server should be accessible as expected.

Additional Tips

• Ensure your Vite server is set to host: true to allow external access from Docker.
• Always expose the correct port in your Dockerfile and Docker Compose file to match the port that Vite is using.

If you have any other questions or need further assistance, feel free to reach out. Happy coding!