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Subnet

A deep dive into Subnet - Practical ver.



What is a Subnet?

  • The IP address range of a VPC
    • It divides the VPC into segments
  • AWS VPC cannot operate without subnets!

Subnet Names

  • It is a conceptual division
    • public
    • private
  • You don't necessarily have to use public or private as subnet names
  • Separating DB subnets is a matter of preference

Subnet CIDR Block

  • Subnets also require a CIDR block to be specified
  • Subnet CIDRs must not conflict with each other
  • Subnet CIDRs must not exceed the VPC range
    • Because the VPC size is the maximum IP constraint!
  • Think of it as claiming territory within the VPC with subnets
    • If a subnet runs out of IPs, you can create another subnet in the unclaimed space!
      • However, when creating resources, there will be two subnet options, so you'll have to decide which subnet to choose...
        • Don't add subnets later -- design it properly from the start!
    • You can add subnets to the unclaimed space in the VPC, but you cannot merge two subnets