Interview Q&A / AWS & Cloud

1. What is a VPC, and what is the difference between public and private subnets?

   A VPC is your own private network inside AWS. A public subnet has a route to an internet gateway, so resources with public IPs can be reached from the internet. A private subnet has no such route; its servers reach the internet only outbound, through a NAT gateway placed in a public subnet.

   IntermediateIn-depth4 min read
2. What is the difference between a security group and a network ACL in AWS?

   A security group is a stateful firewall attached to an instance's network interface, with allow rules only. A network ACL is a stateless firewall on a subnet, with numbered allow and deny rules checked in order. Because NACLs are stateless, you must allow return traffic explicitly, usually on ephemeral ports.

   IntermediateIn-depth4 min read
3. What is an Elastic IP address and how is it different from a normal public IP on EC2?

   A normal public IP is assigned from AWS's pool and can change when the instance is stopped and started. An Elastic IP is a static public IPv4 address you own in your account until you release it and can remap to another instance.

   BeginnerQuick answer1 min read
4. What is the difference between an internet gateway and a NAT gateway?

   An internet gateway lets resources with public IPs in a public subnet talk to the internet in both directions. A NAT gateway lets private-subnet instances start outbound connections, such as updates, while blocking inbound connections from the internet.

   BeginnerQuick answer1 min read
5. What is the difference between VPC peering and AWS Transit Gateway?

   VPC peering is a one-to-one private link between two VPCs and it is not transitive. Transit Gateway is a central hub that connects many VPCs and on-premises networks, so each network connects once.

   IntermediateQuick answer1 min read