How to Combine Host Network with Docker to Resolve IP Connectivity Issues?

I am working on dockerizing my POS system, but I've encountered a challenge. In my setup, I usually store the printer's IP address in the product table of the database, as some products need to be printed on specific thermal printers.

However, after dockerizing the system, the printers are not working. While the data is successfully created in the database, the printers no longer print anything, even though they used to work fine before dockerization.

Here is my Dockerfile:

# Base image 
FROM node:21-slim

# Set working directory 
WORKDIR /app

# Copy package.json and install dependencies 
COPY package*.json ./ 

RUN npm uninstall bcrypt 

RUN npm install pm2 -g && npm install bcrypt && npm install

# Copy application files 
COPY . .

# Copy Prisma schema directory 
COPY prisma ./prisma

# Install required dependencies 
RUN apt-get update -y && apt-get install -y openssl

# Generate Prisma client 
RUN npx prisma generate

# Expose the app's port 
EXPOSE 4000

# Start the app with PM2 
CMD ["pm2-runtime", "ecosystem.config.js"]

docker-compose.yml:

    build:
      context: .
      dockerfile: Dockerfile
    container_name: pos
    ports:
      - "4000:4000"
    env_file:
      - .env
    environment:
      DATABASE_URL: "mysql://root:${DATABASE_PASSWORD}@${IP_ADDRESS}:3306/${DATABASE_NAME}?connection_limit=150&pool_timeout=20"
      ACCESS_TOKEN: "37eb2d015162e05553cae95588485f3b18de5eb95182c97fc0df8293222010028d797515afefbb72b861c637c1288987e3628ed8103641eb53d439e630a90a6d"
      ADMIN_PORT: 4500
      PORT: 4000
      REDIS_URL: "redis://redis:6379"
    depends_on:
      - redis


  redis:
    image: redis:alpine
    container_name: redis ```

Im using tcpIp technique to send orders to printers (node-thermal-printer package): ```
      let printer = new ThermalPrinter({
        type: PrinterTypes.TANCA,
        interface: "tcp://" + printerIp,
        width: 40,
        options: { timeout: 5000 }
      }); 

I have successfully pinged the printer's IP from the Docker container. I also tried setting the network_mode to host in the app's configuration, but this caused a conflict between the app and Redis, as both are on the same network. When I changed the app to use the host network mode, I had to modify the Redis configuration, which I do not want to do.

This one doesn't work as well:

network_mode: "host"
environment:
  REDIS_URL: "redis://172.18.0.2:6379" //CONTAINER'S IP

I managed to fix the issue by following these steps:

1- Modified the docker-compose.yml file to this one:

 services:
   app:
     build:
       context: .
       dockerfile: Dockerfile
     container_name: pos
     ports:
       - "4000:4000"
     env_file:
       - .env
     environment:
       DATABASE_URL: "mysql://root:${DATABASE_PASSWORD}@host.docker.internal:3306/${DATABASE_NAME}?connection_limit=150&pool_timeout=20"
       ACCESS_TOKEN: "37eb2d015162e05553cae95588485f3b18de5eb95182c97fc0df8293222010028d797515afefbb72b861c637c1288987e3628ed8103641eb53d439e630a90a6d"
       ADMIN_PORT: 4500
       PORT: 4000
       REDIS_URL: "redis://redis:6379" # Use service name "redis" for inter-container communication
     depends_on:
       - redis # Ensure Redis starts before the app
     networks:
       - app-network
     volumes:
       - pos:/app

   redis:
     image: redis:alpine
     container_name: redis
     networks:
       - app-network

 networks:
   app-network:
     driver: bridge

 volumes:
   pos:

2- And then pinged to the printer from the docker container through these steps:

Access the container:

docker exec -it <container_name_or_id> /bin/bash

Determine OS:

cat /etc/os-release

In my case it's debian, so I just installed necessary packages to ping the printer's IP address:

apt-get update && apt-get install -y iputils-ping

Then pinged the IP:

ping 192.168.1.100

All requests reached successfully.

exit the container

exit

3- Then modified the Dockerfile, installed some required libraries and packages to my container in order to be able to run Puppeteer and headless browser (I used in the vouchers):

# Base image
FROM node:21-slim

RUN apt-get update && apt-get install -y \
    libglib2.0-0 \
    libnss3 \
    libatk1.0-0 \
    libatk-bridge2.0-0 \
    libcups2 \
    libdrm2 \
    libxkbcommon0 \
    libxcomposite1 \
    libxdamage1 \
    libxfixes3 \
    libxrandr2 \
    libgbm1 \
    libgtk-3-0 \
    libasound2 \
    libxshmfence1 \
    chromium \
    && rm -rf /var/lib/apt/lists/*

# Set working directory
WORKDIR /app

# Copy package.json and install dependencies
COPY package*.json ./

RUN npm install pm2 -g && npm install bcrypt && npm install

# Copy application files
COPY . .

# Copy Prisma schema directory
COPY prisma ./prisma

# Install required dependencies
RUN apt-get update -y && apt-get install -y openssl

# Generate Prisma client
RUN npx prisma generate

# Expose the app's port
EXPOSE 4000

# Start the app with PM2
CMD ["pm2-runtime", "ecosystem.config.js"]