Welcome back to our AWS Cloud Engineer Interview Series! In Part I, we explored advanced scenario-based and behavioral questions—covering topics like VPC design, security best practices, and troubleshooting strategies to demonstrate big-picture architecture skills.
In Part II, we drilled down into core AWS Fundamentals with ten targeted questions on Compute Services, Storage Options, and Database Services, complete with frameworks for structuring your answers and real-world examples.
Now in Part 3, we turn our focus to Networking & Security—the lifeblood of any well-architected AWS environment. You’ll find ten common interview questions on VPC design, routing, NAT gateways, Security Groups vs. NACLs, and IAM. Each question includes explanations, interview framing, and real-world examples.
1. Designing a VPC with Public and Private Subnets
How to Answer
- VPC Scope: Define CIDR block (e.g., 10.0.0.0/16)
- Subnets: Split across AZs (e.g., 10.0.1.0/24, 10.0.2.0/24)
- Public Subnets: Route to Internet Gateway
- Private Subnets: No direct IGW access
- NAT Gateway: One per AZ for high availability
Example: Multi-AZ architecture with NAT gateways for outbound access from private subnets.
2. Route Tables Explained
How to Answer
- Route tables define traffic direction
- Public: 0.0.0.0/0 → IGW
- Private: 0.0.0.0/0 → NAT Gateway
- Default local routing enables subnet communication
3. Public vs Private Subnets
- Public: Internet access via IGW
- Private: No direct internet access
- Internet Access: Via NAT Gateway
4. 3-Tier Architecture Security
- Web Tier: Public subnet (ALB)
- App Tier: Private subnet
- DB Tier: Isolated subnet
Use security groups for tier isolation and least privilege.
5. Security Groups vs NACLs
- Security Groups: Stateful, allow-only
- NACLs: Stateless, allow + deny
- Use SGs: Default control
- Use NACLs: Broad subnet-level filtering
6. Rule Evaluation Differences
- SG: No order, any match allows
- NACL: Ordered rules, first match wins
7. Securing a Database
- DB in private subnet
- Allow access only from app layer SG
- No public exposure
8. When to Use NACLs
- Block malicious IP ranges
- Subnet-wide restrictions
- Explicit deny rules
9. IAM Concepts
- User: Individual identity
- Group: Collection of users
- Role: Temporary access
- Policy: Permission definition
10. IAM Best Practices
- Use least privilege
- Enable MFA
- Use roles instead of access keys
- Rotate credentials
- Use AWS Organizations for control
Final Tips
- Be precise with AWS terminology
- Use real-world examples
- Apply STAR method
- Align with AWS best practices
By mastering these topics, you’ll be ready to demonstrate strong AWS Networking & Security expertise in interviews.
