10 AWS Scenario-Based Interview Questions with Answers

Question: You need to design a VPC architecture for a two-tier application that must be highly available and scalable. How would you design this VPC architecture?

Answer: To design a highly available and scalable two-tier application architecture in a VPC:

• Create a VPC with public and private subnets across multiple Availability Zones (AZs).

• Place load balancers in the public subnets to handle incoming traffic.

• Deploy application servers in private subnets across multiple AZs.

• Use Auto Scaling groups for the application servers to ensure scalability.

• Implement security groups and network ACLs for proper security.

Question: Your organization has a VPC with multiple subnets. You want to restrict outbound internet access for resources in one subnet but allow outbound internet access for resources in another subnet. How would you achieve this?

Answer: To control outbound internet access for different subnets:

• Modify the route table associated with the subnet that needs restricted access.

• Remove the default route (0.0.0.0/0) that points to the Internet Gateway for the restricted subnet.

• Keep the default route intact for the subnet that needs internet access.

• Alternatively, use Network ACLs to control outbound traffic at the subnet level.

Question: You have a VPC with public and private subnets. Instances in the private subnet need access to the internet for software updates. How would you allow internet access for instances in the private subnet?

Answer: To provide internet access for instances in a private subnet:

• Set up a NAT Gateway in the public subnet.

• Update the route table for the private subnet to direct internet-bound traffic (0.0.0.0/0) to the NAT Gateway.

• This allows instances in the private subnet to access the internet for updates while remaining private and secure.

Question: You have launched EC2 instances in your VPC and you want them to communicate with each other using private IP addresses. What steps would you take to enable this communication?

Answer: To enable communication between EC2 instances using private IP addresses:

• Ensure all instances are in the same VPC.

• Configure security groups to allow inbound and outbound traffic on the necessary ports between the instances.

• If instances are in different subnets, ensure the route tables allow communication between the subnets.

• Use private IP addresses for communication within the VPC.

Question: You want to implement strict network access control for your VPC. How would you achieve this?

Answer: To implement strict network access control:

• Use Network ACLs (NACLs) at the subnet level to control inbound and outbound traffic.

• Configure security groups for EC2 instances to provide an additional layer of security.

• Implement least privilege access by only opening necessary ports and protocols.

• Use VPC Flow Logs to monitor network traffic for security analysis.

• Consider using AWS WAF for additional protection against web exploits.

Question: Your organization requires an isolated environment within the VPC for running sensitive workloads. How do you set up this isolated environment?

Answer: To set up an isolated environment for sensitive workloads:

• Create a separate subnet within the VPC for the sensitive workloads.

• Use a dedicated route table for this subnet, ensuring no route to the internet gateway.

• Implement strict Network ACLs to control traffic in and out of the subnet.

• Use VPC endpoints for necessary AWS services to avoid traffic leaving the Amazon network.

• Implement additional security measures like encryption and monitoring.

Question: Your application needs access to AWS services such as S3 to communicate securely within the VPC. How would you achieve this?

Answer: To allow secure access to AWS services from within a VPC:

• Use VPC Endpoints, specifically Gateway Endpoints for services like S3 and DynamoDB.

• For other services, use Interface Endpoints (powered by AWS PrivateLink).

• Configure the VPC's route table to direct traffic for the AWS service to the VPC Endpoint.

• Update security groups to allow traffic to and from the VPC Endpoint.

Question: What is the difference between Network ACLs and Security Groups?

Answer: Key differences between Network ACLs and Security Groups:

• Network ACLs operate at the subnet level, while Security Groups operate at the instance level.

• NACLs are stateless (return traffic must be explicitly allowed), while Security Groups are stateful.

• NACLs process rules in order, with an implicit deny at the end. Security Groups evaluate all rules before deciding.

• NACLs can have deny rules, while Security Groups can only allow traffic.

• NACLs are a good first line of defense, while Security Groups provide more fine-grained control.

Question: What is the difference between IAM users, groups, roles, and policies?

Answer:

• IAM Users: Individual identities for people or services that need AWS access.

• IAM Groups: Collections of IAM users, making it easier to manage permissions for multiple users.

• IAM Roles: Identity with permissions that can be assumed by users, applications, or services.

• IAM Policies: Documents defining permissions, attached to users, groups, or roles to specify allowed actions.

Question: You have a private subnet in a VPC that contains a number of instances that should not have direct internet access. However, you still need to be able to securely access these instances for administrative purposes. How would you set up a bastion host to facilitate this access?

Answer: To set up a bastion host for secure access to private instances:

• Launch a bastion host (jump server) in a public subnet of your VPC.

• Configure security groups to allow SSH (for Linux) or RDP (for Windows) access to the bastion host from your IP.

• Set up security groups for private instances to allow inbound SSH/RDP traffic only from the bastion host.

• Use SSH agent forwarding or SSH tunneling for secure key management.

• Implement additional security measures like multi-factor authentication and detailed logging on the bastion host.