Hey there, let's work through that "cannot find module 'express'" error you're hitting while containerizing your Node-RED app!

问题根源 #

Your current Dockerfile uses debian:stretch-slim as the base image, which only includes a minimal Debian system—no pre-installed Node.js, npm, or any of the dependency packages (like express) that Node-RED needs. When the container starts up, Node.js can't locate these missing dependencies, hence the error.

修复步骤 #

1. Pick a more suitable base image #

The easiest way to avoid manual setup headaches is to use an official Node.js image, which comes pre-configured with Node.js and npm. For Debian stretch compatibility, go with node:8-stretch (Node-RED works reliably with Node.js 8.x for this system version).

2. Full Dockerfile example #

Replace your existing Dockerfile with this version—each step is commented for clarity:

# Use official Node.js 8 image (built on Debian stretch)
FROM node:8-stretch

# Create Node-RED user and home directory (matches your original setup)
RUN useradd -c 'Node-Red user' -m -d /home/nodered -s /bin/bash nodered

# Set working directory to Node-RED user's home
WORKDIR /home/nodered

# Copy your local Node-RED source code into the container
# Adjust the source path if your code isn't in your current local directory
COPY . .

# Switch to nodered user to install dependencies (avoids root permission risks)
USER nodered

# Install all Node-RED dependencies (including express)
RUN npm install

# Expose Node-RED's default port
EXPOSE 1880

# Start Node-RED when the container launches
CMD ["npm", "start"]

3. If you want to stick with debian:stretch-slim #

If you prefer to use the slim Debian base, you'll need to manually install Node.js and npm first. Add these steps early in your Dockerfile:

FROM debian:stretch-slim

# Install Node.js and npm, then clean up apt cache to reduce image size
RUN apt-get update && apt-get install -y nodejs npm && \
    apt-get clean && rm -rf /var/lib/apt/lists/*

# Follow with your existing steps: create user, copy source code, install dependencies, etc.

Note that this approach requires more system-level configuration, so the official Node.js image is still the simpler option.

4. Build and run your container #

Execute these commands to build your image and start the container:

# Build the image (replace "your-nodered-image" with a name you prefer)
docker build -t your-nodered-image .

# Start the container, mapping port 1880 to your host machine
docker run -p 1880:1880 your-nodered-image

Once the container is running, you should be able to access Node-RED at http://localhost:1880 without the express module error.

内容的提问来源于stack exchange，提问作者Kaushik Nandy