Subnet

💡 Definition

A Subnet is a range of IP addresses in your VPC. You launch AWS resources (like EC2 instances) into a specific subnet. Use a public subnet for resources that must be connected to the internet, and a private subnet for resources that won't be connected to the internet.

🔑 Key Concepts

• VPC Partition: Divides a VPC into smaller networks.
• AZ Specific: A subnet resides entirely within one AZ; it cannot span zones.
• Public Subnet: Has a route to an Internet Gateway.
• Private Subnet: Does not have a direct route to the internet. Uses a NAT Gateway for outbound access.

⚙️ How it Works

1. Create VPC: Define the main CIDR block (e.g., 10.0.0.0/16).
2. Create Subnet: Define a smaller CIDR block (e.g., 10.0.1.0/24) and select an AZ.
3. Route Table: Associate the subnet with a route table that determines where traffic goes.

🎯 Use Cases

• Isolation: Separating public-facing web servers from backend database servers.
• High Availability: Creating subnets in different AZs to deploy redundant resources.

💰 Pricing Model

• Free: There is no additional charge for creating subnets.

📝 Exam Tips (CLF-C02)

• Subnets map to a single Availability Zone.
• Public vs. Private depends on the Route Table (specifically, a route to the IGW).
• 5 IP addresses are reserved by AWS in every subnet.

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See Also: * VPC * Internet Gateway * NAT Gateway * Route Table