Using GCP Artifact Registry incurs small costs, and Docker Hub allows only one private repository on the free tier.

This guide explains how to build Docker images on a development PC, push them to a local registry on a LAN, and deploy them to a test server without cloud costs.

Background

Previously, the test environment built everything directly on the test laptop:

[Old Approach]
Test Laptop: git pull → mvn build → docker build → docker run

Problems:

• Requires full build environment (JDK, Maven, Node.js, etc.) on the test server
• Slow build times
• Risk of inconsistent environments

Improved approach:

[Improved Approach]
Dev PC: code change → build-push.sh → push to local registry
Test Server: docker-compose pull → docker-compose up

Environment Setup

Role	Machine	OS
Dev PC	750XDA	Ubuntu
Test Server	GU502DU	Ubuntu

• Test server IP: 192.168.1.144
• Registry port: 5000

Step 1: Install Docker Registry on Test Server

Create a dedicated user

sudo useradd -m -s /bin/bash dkr
sudo usermod -aG docker dkr
sudo usermod -aG sudo dkr

Open firewall port

sudo ufw allow 5000/tcp
sudo ufw status

Run registry container

su - dkr

docker run -d \
  -p 5000:5000 \
  --restart=always \
  --name registry \
  registry:2

Verify

curl http://192.168.1.144:5000/v2/_catalog

Expected:

{"repositories":[]}

Step 2: Configure Insecure Registry (Dev PC)

sudo tee /etc/docker/daemon.json <<EOF
{
  "insecure-registries": ["192.168.1.144:5000"]
}
EOF

sudo systemctl restart docker

Step 3: Build & Push Services

Java / Spring Boot

./mvnw clean package -DskipTests

docker build -t 192.168.1.144:5000/user-service:latest .
docker push 192.168.1.144:5000/user-service:latest

Frontend (Next.js)

./docker-build.sh

docker tag frontend:latest 192.168.1.144:5000/frontend:latest
docker push 192.168.1.144:5000/frontend:latest

Python / FastAPI (with BuildKit Secret)

DOCKER_BUILDKIT=1 docker build \
  --secret id=gcp_sa_key,src=/path/to/key.json \
  -t 192.168.1.144:5000/chat-service:latest \
  .

docker push 192.168.1.144:5000/chat-service:latest

Step 4: build-push.sh Script

Example:

#!/bin/bash
set -e

REGISTRY="192.168.1.144:5000"
IMAGE="user-service"

./mvnw clean package -DskipTests

docker build -t ${REGISTRY}/${IMAGE}:latest .
docker push ${REGISTRY}/${IMAGE}:latest

Step 5: Verify Registry

curl http://192.168.1.144:5000/v2/_catalog

Docker Hub vs Local Registry

Feature	Local Registry	Docker Hub
Cost	Free	Limited
Speed	Fast (LAN)	Slower
Security	Internal	External

Automatic Deployment with Watchtower

Until now, deployment required manually running:

docker-compose pull
docker-compose up -d

We can automate this using Watchtower.

What is Watchtower?

Watchtower monitors running containers and automatically updates them when a new image is available.

Install Watchtower

On the test server:

docker run -d \
  --name watchtower \
  -v /var/run/docker.sock:/var/run/docker.sock \
  containrrr/watchtower \
  --interval 30

• Checks for updates every 30 seconds

Optional: Enable per-service updates

services:
  user-service:
    image: 192.168.1.144:5000/user-service:latest
    labels:
      - "com.centurylinklabs.watchtower.enable=true"

Run Watchtower with:

--label-enable

How It Works

Dev PC → build-push.sh → push to registry

Test Server:
Watchtower detects new image
→ pulls image
→ restarts container automatically

Advantages

• No manual deployment needed
• Near real-time updates
• Simple setup
• Works without full CI/CD pipeline

Considerations

1. Using latest may cause caching issues
   → Prefer versioned tags (e.g., :20260324-1)
2. Containers are restarted automatically
   → Not zero-downtime by default
3. For production:
   • Add validation
   • Add rollback strategy

Final Result

With this setup: 👉 Push from Dev PC automatically updates the test server.

Simple, fast, and cost-free deployment inside your LAN.