AWS VPC Networking: Subnets, NAT Gateways, Transit Gateway, and PrivateLink
AWS networking is the foundation that everything else sits on, yet it is the area where most teams accumulate the most technical debt. A poorly designed VPC leads to security gaps, connectivity issues, and painful migrations later. Getting your network architecture right from the start - proper CIDR planning, subnet tiers, and connectivity patterns - saves enormous headaches as you scale.
Every production VPC should have three subnet tiers across multiple availability zones: public subnets for load balancers and bastion hosts, private subnets for application workloads, and isolated subnets for databases with no internet access. NAT Gateways provide outbound internet access for private subnets - deploy one per AZ for high availability, but be aware they are one of the most expensive networking components. Use VPC endpoints (Gateway endpoints for S3/DynamoDB, Interface endpoints for other services) to keep traffic on the AWS backbone and reduce NAT Gateway costs.
For multi-VPC architectures, Transit Gateway replaces the mesh of VPC peering connections that becomes unmanageable beyond 3-4 VPCs. Transit Gateway acts as a hub that all VPCs connect to, with route tables controlling which VPCs can communicate. PrivateLink exposes services across VPCs or to customers without traversing the public internet - essential for SaaS architectures and shared services platforms. Plan your CIDR ranges carefully to avoid overlaps, and use AWS RAM to share subnets across accounts in an AWS Organizations setup.
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