cdk/cloudformation 如何理解哪个 su.net 是私有的还是公共的？

Question

I have three su.nets in AWS.

One is public because it has inte.net-gateway

And other two are not.

However when cdk synth, there comes template cdk.context.json

It judges every three su.nets are Public

However other two are Isolated in fact(without NAT gateway and public IP)

Why cdk think they are Public ??

  "vpc-provider:account=678100XXXXXX:filter.vpc-id=vpc-0867d6797e62dd78b:region=ap-northeast-1:returnAsymmetricSubnets=true": {
    "vpcId": "vpc-0867d6797e62dd78b",
    "vpcCidrBlock": "10.0.0.0/24",
    "availabilityZones": [],
    "subnetGroups": [
      {
        "name": "Public",
        "type": "Public",
        "subnets": [
          {
            "subnetId": "subnet-0b5985476dee1f20c",
            "cidr": "10.0.0.0/25",
            "availabilityZone": "ap-northeast-1c",
            "routeTableId": "rtb-02a749d8d4415bbfb"
          },
          {
            "subnetId": "subnet-0fdd37150bfff91f0",
            "cidr": "10.0.0.128/26",
            "availabilityZone": "ap-northeast-1c",
            "routeTableId": "rtb-02a749d8d4415bbfb"
          },
          {
            "subnetId": "subnet-085c85398f27adbfd",
            "cidr": "10.0.0.192/26",
            "availabilityZone": "ap-northeast-1d",
            "routeTableId": "rtb-02a749d8d4415bbfb"
          }
        ]
      }
    ]
  }
}

Answer 1

Whether a su.net is public or private is determined by its route tables only. Public su.nets will have route tables to the inte.net gateway , whereas private su.nets will not. Instead private su.nets may have routes to NAT gateways, but this still does not make them public su.nets.