CDK-3TA

CDK example on how to build a Web 3 Tier Architecture. It is an example for training purpose DON'T USE IT IN PRODUCTION. Project's location: https://github.com/rluberti/CDK-3TA/

Introduction

The AWS Cloud Development Kit (AWS CDK) is an open source software development framework to define your cloud application resources using familiar programming languages (see https://aws.amazon.com/cdk/). This project is a basic example in Python on how to create a classic Web 3 Tier Architecture (Web / App / DB Tiers, see https://en.wikipedia.org/wiki/Multitier_architecture#Three-tier_architecture).

Features

• Internet public open entrypoint is handled by an Application Load Balancer
• Web/App/DB tiers are on PRIVATE subnets with traffic to internet limited to OUTBOUND only
• Web and App tiers are in autoscaling (min 2 instances to max 4) based on CPU % usage (target is 40%)
• DB tier is a RDS MySQL in multi AZ (see https://aws.amazon.com/rds/mysql/)
• Architecture is contained in one VPC and it is in High Availability using two Availability Zones (AZ)
• Admin access to EC2 instances is only allowed via Session Manager Session. No open inbound ports and no need to manage bastion hosts or SSH keys (see https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager.html)
• Application logic is provided by some simple code in Pythoin using Flask (see https://flask.palletsprojects.com/en/2.0.x/)
• RDS connectivity credentials and URL path stored using AWS Secret Manager (https://aws.amazon.com/secrets-manager/)
• Web and App applications are streaming their custom logs using "Log streams" created in the "CDK-3TA-EC2-LOG-GROUP" Log group on CloudWatch console page.
• VPC is logging internal network activity via "Flow log" created in "CDK-3TA-VPC-FLOWLOG-GROUP" Log group (see https://docs.aws.amazon.com/vpc/latest/userguide/flow-logs.html).

Installation

Requirements

• AWS CLI (see https://docs.aws.amazon.com/cli/latest/userguide/install-cliv2-mac.html) or just use AWS Cloud Shell (see https://aws.amazon.com/cloudshell/)
• CDK (see https://docs.aws.amazon.com/cdk/latest/guide/cli.html)
• Python 3.x
• git

Steps

• Clone repository
• git clone https://github.com/rluberti/CDK-3TA.git
• Create Python Virtual Environment
• cd CDK-3TA
• python3 -m venv .venv
• Run Virtual Environment
• source .venv/bin/activate
• Install Python packages
• pip3 install aws-cdk.aws-codedeploy aws-cdk.aws-rds
• Check if CDK can create CloudFormation code running:
• cdk synth
• Create Stack deploying the code on AWS CloudFormation:
• cdk deploy
• It will display the Web public DNS entry point as "CDK-3TA-Stack.WebALBDNS"
• Delete Stack
• cdk destroy

Usage

• Use http://<CDK-3TA-Stack.WebALBDNS>/ to hit the Web tier only and get its output
• Use http://<CDK-3TA-Stack.WebALBDNS>/app to hit Web tier first, then App tier and get its ouput
• Use http://<CDK-3TA-Stack.WebALBDNS>/db to hit Web tier first, App tier second and DB tier at the end with its output
• Connect via SSM session to any EC2 instance and run utility stress --cpu 2 to make total CPU utilization spike to over 40% and trigger scaling up to 4 instances.