Subnets and Route Tables in Depth

~14 min read

How a route table's target field is the single source of truth for whether a subnet is public or private.

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Key points

  • The 'local' route is automatic and lets resources in the VPC reach each other regardless of subnet
  • A subnet is public or private purely based on its route table's 0.0.0.0/0 target — not a label or setting
  • Best practice: explicit route tables per tier, never leave production subnets on the default main route table
  • Multiple subnets across AZs can share one route table if they need identical routing behavior