What is a VPC and what are its main building blocks?

What the interviewer wants to hear

• A logically isolated private network in the cloud
• Defined by a CIDR range and divided into subnets per AZ
• Route tables, internet gateway and NAT gateway control traffic flow
• Security groups and NACLs filter traffic
• Public vs private subnets

Model answer

A VPC, or Virtual Private Cloud, is a logically isolated network inside a cloud provider where you launch your resources. You give it an IP range in CIDR notation, such as 10.0.0.0/16, and split that into subnets, each living in one availability zone. Route tables decide where traffic goes. A public subnet has a route to an internet gateway, while a private subnet usually sends outbound traffic through a NAT gateway so instances can download updates without being reachable from outside. Security groups act as stateful firewalls on each network interface, and network ACLs are stateless filters at the subnet level. You can also add VPC endpoints for private access to services like S3, and connect VPCs using peering or a transit gateway. A common pattern is load balancers in public subnets and apps and databases in private subnets across at least two AZs.

More easy Cloud Engineer questions

• Explain the difference between IaaS, PaaS and SaaS with an example of each.
• Explain IAM users, groups, roles and policies. When would you use a role instead of a user?
• How would you make a simple web application highly available in the cloud?
• What pricing models do cloud providers offer for compute, and when would you use each?
• What is the difference between containers and virtual machines, and when would you choose each?
• What is Infrastructure as Code and why do teams use it instead of the cloud console?
• Explain metrics, logs and traces. How does each help you run a cloud application?
• How does a CDN work, and what should you consider when caching content with one?
• Compare block, object and file storage in the cloud. Give a use case for each.