🚀 DevSecOps Journey — Day 17

Building Real 3-Tier Applications with Databases (Hands-on)

Yesterday, I explored project architecture and build systems.
Today, I moved one step closer to real production systems by working on 3-Tier applications.

This learning focused on how applications connect to databases, how credentials are handled, and what a DevOps engineer must know beyond just running code.

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🧱 2-Tier vs 3-Tier Architecture (Simple Explanation)

🔹 2-Tier Architecture

• Application layer

• Database layer

👉 Suitable for small or simple systems.

🔹 3-Tier Architecture

• 🖥 Presentation Layer – UI / Client

• ⚙️ Business Layer – Application logic

• 🗄 Database Layer – Data storage

👉 Used in production environments for:

• Better security

• Scalability

• Maintainability

As a DevOps engineer, understanding database setup, users, passwords, tables, and connectivity is essential.

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☕ Project #6: 3-Tier Java + MySQL Application

🔧 System Preparation

sudo apt update
sudo apt upgrade -y

Ensures latest packages and security patches.

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🗄 Installing MySQL

sudo apt install mysql-server -y

• Database connection details live in application.properties

• Best practice:

  • Store DB user, password, and URL in:

    • Environment variables

    • Secret managers (Vault, AWS Secrets Manager)

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▶️ MySQL Service Management

systemctl status mysql
sudo systemctl start mysql
sudo systemctl enable mysql

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🔐 Securing MySQL (Optional for Local)

sudo mysql_secure_installation

This helps with:

• Removing anonymous users

• Disabling remote root login

• Removing test databases

  

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🧑‍💻 Database & User Setup

CREATE DATABASE bankappdb;

CREATE USER 'adi'@'localhost' IDENTIFIED BY 'Test@123';
ALTER USER 'adi'@'localhost' IDENTIFIED WITH mysql_native_password BY 'Test@123';
GRANT ALL PRIVILEGES ON bankappdb.* TO 'adi'@'localhost';
FLUSH PRIVILEGES;

💡 Switching to mysql_native_password avoids the common JDBC error:
“Public Key Retrieval is not allowed”

🔗 GitHub – Project #6 (Java + MySQL):
👉 https://github.com/Jysh06/3-Tier-Java-MySQL-Database

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🌐 Project #7: 3-Tier Node.js + MySQL Application

🗄 Database Setup

• MySQL installation & configuration

• Database and table creation (users)

• Credentials stored in db.js

CREATE DATABASE test_db;

CREATE TABLE users (
  id INT AUTO_INCREMENT PRIMARY KEY,
  name VARCHAR(255),
  email VARCHAR(255) UNIQUE,
  role ENUM('Admin','User')
);

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🖥 Client Setup

cd client
npm install
npm run build

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⚙️ Server Setup

cd server
npm install
npm start

📍 App runs on: http://localhost:5000

This project clearly showed how backend services depend on database readiness.

🔗 GitHub – Project #7 (Node.js + MySQL):
👉 https://github.com/Jysh06/3-Tier-NodeJS-MySQL-Database

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🔷 Project #8: 3-Tier .NET + MongoDB Application

This project introduced NoSQL databases.

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⚙️ Installing .NET

sudo apt install dotnet-sdk-8.0 aspnetcore-runtime-8.0 -y

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🗄 Installing MongoDB

sudo apt install mongodb-org -y
sudo systemctl enable mongod
sudo systemctl start mongod

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📂 MongoDB Shell Usage

mongosh
show dbs
use db_name
show collections
db.Products.find().pretty()

• DB credentials stored in appsettings.json

  

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▶️ Running the App

dotnet restore
dotnet build
dotnet run

🔗 GitHub – Project #8 (.NET + MongoDB):
👉 https://github.com/Jysh06/3-Tier-DotNet-MongoDB

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🐍 Project #9: 3-Tier Python + PostgreSQL Application

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🧪 Python Virtual Environment

sudo apt install python3.12-venv -y
python3 -m venv myenv
source myenv/bin/activate
pip install -r requirements.txt

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🗄 PostgreSQL Setup

sudo apt install postgresql postgresql-contrib
sudo systemctl start postgresql
sudo systemctl enable postgresql

CREATE USER root WITH PASSWORD 'root';
CREATE DATABASE my_database;
GRANT ALL PRIVILEGES ON DATABASE my_database TO root;

• DB details stored in config.py

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▶️ Running the Application

source myenv/bin/activate
python run.py

🔗 GitHub – Project #9 (Python + PostgreSQL):
👉 https://github.com/your-username/python-postgres-3tier

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🔐 DevSecOps Perspective: Credential Management

Across all projects:

• ❌ Avoid hardcoding credentials

• ✅ Use:

  • Environment variables

  • Secrets managers

This is a core DevSecOps principle.

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✅ Day 17 Summary

Today I worked with:

• ☕ Java + MySQL

• 🌐 Node.js + MySQL

• 🔷 .NET + MongoDB

• 🐍 Python + PostgreSQL

And learned:

• 2-Tier vs 3-Tier architecture

• SQL vs NoSQL basics

• Database installation & security

• User, password & permission handling

• Application–database integration

This hands-on experience strengthened my understanding of how real production systems are built and operated.