Cloud Networking (VPC) Basics Cheat Sheet
Covers VPC fundamentals including subnets, route tables, security groups, NAT gateways, and peering using AWS terminology.
2 PagesIntermediateFeb 12, 2026
Core VPC Components
The building blocks of a Virtual Private Cloud.
- VPC- An isolated virtual network within a cloud region, defined by a CIDR block (e.g. 10.0.0.0/16)
- Subnet- A range of IPs within a VPC, tied to a single Availability Zone
- Public Subnet- Has a route to an Internet Gateway for direct internet access
- Private Subnet- No direct route to the internet; outbound traffic goes through a NAT Gateway
- Route Table- Set of rules determining where network traffic from a subnet is directed
- Internet Gateway (IGW)- Allows communication between VPC resources and the internet
- NAT Gateway- Lets private subnet resources initiate outbound internet traffic without being reachable inbound
Security Layers
How traffic is filtered at different layers of a VPC.
- Security Group- Stateful, instance-level firewall; allow rules only, evaluated as a whole
- Network ACL (NACL)- Stateless, subnet-level firewall; supports both allow and deny rules, evaluated in order
- VPC Peering- Direct network connection between two VPCs, non-transitive
- Transit Gateway- Hub-and-spoke connector for many VPCs and on-prem networks, supports transitive routing
- VPC Endpoint- Private connectivity to AWS services (S3, DynamoDB) without traversing the public internet
Minimal VPC in Terraform
Creating a VPC with a public subnet and internet gateway.
hcl
resource "aws_vpc" "main" { cidr_block = "10.0.0.0/16"}resource "aws_subnet" "public" { vpc_id = aws_vpc.main.id cidr_block = "10.0.1.0/24" map_public_ip_on_launch = true availability_zone = "us-east-1a"}resource "aws_internet_gateway" "igw" { vpc_id = aws_vpc.main.id}resource "aws_route_table" "public" { vpc_id = aws_vpc.main.id route { cidr_block = "0.0.0.0/0" gateway_id = aws_internet_gateway.igw.id }}
Pro Tip
Size your VPC CIDR generously (a /16) even for small workloads — subnets are cheap to create but resizing a VPC's CIDR later requires painful re-architecture or secondary CIDR blocks.
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