See the Explanation for complete solution for this task.
Explanation:
A diagram of a computer AI-generated content may be incorrect.

Step 1: Understand Requirements & Security Principles
Requirements:
* Customer-facing payment application (PCI DSS compliance applies)
* Hosted on third-party cloud (e.g., AWS)
* Must segment public-facing and internal resources
* Needs to be scalable and resilient
* Must have strong security controls
Step 2: Design the High-Level Network Layout
Core Components:
* VPC (Virtual Private Cloud): Isolates your environment from other tenants in the cloud.
* Subnets:
* Public subnet: For resources that must communicate with the internet.
* Private subnet: For internal resources, NOT directly exposed to the internet.
Step 3: Place Resources in Appropriate Subnets
Public Subnet:
* Internet-facing Load Balancer (LB): Distributes traffic to application servers.
* Web Application Firewall (WAF): Protects against web exploits.
* Autoscaling Instances: EC2 (or VM) servers running your web front-end, automatically scaling as traffic grows.
Private Subnet:
* Application servers: Back-end logic, not exposed to internet directly.
* Database: Sensitive data storage, only accessible by application servers.
* Internal Load Balancer: Manages traffic among app servers.
* WAF: Can be used internally as well for defense-in-depth.
Step 4: Add Connectivity and Security Controls
* Internet Gateway: Allows resources in public subnet to communicate with the internet.
* NAT Gateway: Allows outbound internet traffic from private subnet without exposing private IPs.
* Security Groups: Firewalls at the instance level; allow only necessary traffic (e.g., LB to web server, web server to DB).
* Network ACLs: Subnet-level firewalls for additional control.
Step 5: Network Diagram Explanation (Based on Your Images)
Public Subnet (Top Layer)
* Load Balancer
* Accepts HTTPS traffic from customers.
* Sends only necessary HTTP/HTTPS to web servers in public subnet.
* WAF (Web Application Firewall)
* Sits in front of Load Balancer.
* Filters malicious requests (SQLi, XSS, etc.).
* Autoscaling Group
* Multiple web servers for redundancy and scalability.
* Placed in public subnet to respond to traffic spikes.
Private Subnet (Bottom Layer)
* Application Servers
* Receive requests from public subnet's load balancer.
* Not directly exposed to the internet.
* Database
* Only accessible from application servers, never public.
* Security groups restrict all inbound traffic except from app servers.
* Internal Load Balancer
* Balances requests to application servers.
Step 6: Flow of Data (Step-by-Step)
* Client -> Internet Gateway -> WAF -> Load Balancer (Public Subnet):Customers initiate connections to your app over the internet.
* Load Balancer -> Autoscaling Web Servers (Public Subnet):Load balancer routes requests to available web servers.
* Web Servers -> Application Logic (Private Subnet):Web servers pass necessary requests to the internal application servers.
* App Servers -> Database (Private Subnet):Application servers query/update customer payment data in the database.
* Outbound (NAT Gateway):App servers may need to access updates or external APIs-use NAT Gateway for secure outbound connections.
Step 7: Security Best Practices
* Security Groups: Only allow necessary ports (e.g., 443 for HTTPS to LB, 3306 for MySQL between app server and DB).
* Network ACLs: Add another layer of subnet-level restrictions.
* Encryption: Use HTTPS for all external connections, encrypt data at rest and in transit (TLS, disk encryption).
* IAM Roles/Policies: Principle of least privilege for accessing resources.
* Monitoring/Logging: Enable VPC flow logs, cloud service logs, and application logging.
* Patch Management: Automate patching for OS and applications.
* Backups: Regular, secure backups of critical data.
Step 8: Compliance Considerations
For payment applications (PCI DSS):
* Isolate cardholder data environment (CDE).
* Strong access controls (multi-factor authentication, role separation).
* Regular vulnerability assessments and penetration testing.
* Retain logs for auditing.
Step 9: Draw the Architecture (Summary)
* Internet Gateway: Allows inbound/outbound internet access.
* Public Subnet: WAF, Load Balancer, Autoscaling group.
* Private Subnet: App servers, DB, internal LB.
* NAT Gateway: Outbound access for private resources.
* Security Groups/ACLs: Control all traffic flows.
* Monitoring/Logging: Enabled at all levels.
Bonus: Sample Security Group Rules
Web Server (Public Subnet):
* Inbound: 443 (HTTPS) from Internet
* Outbound: 80/443 to App Servers
App Server (Private Subnet):
* Inbound: 80/443 from Web Servers
* Outbound: 3306 (MySQL) to Database
Database (Private Subnet):
* Inbound: 3306 from App Servers
* Outbound: None (unless replication required)
References to Security+ Domains
* 1.0 General Security Concepts: Principle of least privilege, defense in depth.
* 2.0 Threats, Vulnerabilities, Mitigations: WAF, segmentation, patching.
* 3.0 Security Architecture: Network segmentation, secure design.
* 4.0 Security Operations: Monitoring, logging, response.
* 5.0 Security Program Management: Compliance, policy.