1️⃣ Import Libraries

from flask import Flask, jsonify

import pymysql

Flask: Python framework to build web APIs.

jsonify: Converts Python data (like dicts/lists) into JSON responses for HTTP requests.

pymysql: Python library to connect to a MySQL database (in your case, AWS RDS).

2️⃣ Create Flask App

app = Flask(__name__)

Initializes the Flask application.

app is the main object that handles HTTP routes.

3️⃣ Database Configuration

RDS_HOST = 'database-1.c8lweogi44to.us-east-1.rds.amazonaws.com' # master endpoint

RDS_USER = 'admin'

RDS_PASSWORD = 'cloud123'

RDS_DB_NAME = 'dev'

TABLE_NAME = 'users'

These variables store the RDS master database connection details.

TABLE_NAME is the table you want to query (users).

Note: You are using the master/writer endpoint, not a reader endpoint. That means you can read and write data here.

4️⃣ GET API Route to Fetch Users

@app.route('/users', methods=['GET'])

def get_users():

This defines a GET API at /users.

When someone makes a GET request (like via curl or browser), this function runs.

4a. Connect to RDS

connection = pymysql.connect(

host=RDS_HOST,

user=RDS_USER,

password=RDS_PASSWORD,

database=RDS_DB_NAME,

cursorclass=pymysql.cursors.DictCursor # rows as dict

)

Opens a connection to your RDS database.

Cursor ensures each row returned is a Python dictionary (column names → keys).

4b. Execute SQL Query

with connection.cursor() as cursor:

cursor.execute(f"SELECT * FROM {TABLE_NAME} LIMIT 10;")

users = cursor.fetchall()

with connection.cursor() as cursor: Opens a cursor to run SQL queries.

SELECT * FROM users LIMIT 10: Fetches the first 10 rows from your users table.

cursor.fetchall(): Returns all rows as a list of dictionaries.

Example return from users:

[

{"id": 1, "name": "John Doe", "email": "john@example.com"},

{"id": 2, "name": "Alice Smith", "email": "alice@example.com"}

]

4c. Return JSON Response

return jsonify(users)

Converts the Python list of dictionaries into JSON.

This is what the client (browser, curl, Postman) will see.

4d. Error Handling

except Exception as e:

return jsonify({"error": str(e)}), 500

If anything goes wrong (like DB connection fails), return a 500 error with the error message.

4e. Close Connection

finally:

if 'connection' in locals():

connection.close()

Ensures the database connection is closed, even if there’s an error.

Good practice to avoid hanging connections.

5️⃣ Health Check Route

@app.route('/')

def index():

return "RDS Master API running"

Basic GET endpoint at / to check if the Flask app is running.

You can visit http://<your-ec2-ip>:5000/ to see the message.

6️⃣ Entry Point

if __name__ == '__main__':

app.run(host='0.0.0.0', port=5000, debug=True)

Runs the Flask app when you execute the script.

host='0.0.0.0': Makes the API accessible from outside the EC2 instance.

port=5000: The port where the API listens.

debug=True: Enables debugging (auto-reload and detailed error messages).