Cloud Gateway

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A gateway refers to the route that instances within a VPC subnet use to establish communications with other subnets in the same VPC, subnets in other VPCs, or over the Internet.

• Each subnet within a VPC can either be private or public
• To configure a public subnet:
  1. Internet gateway (virtual router) must be attached to the VPC configuration
     • performs 1:1 NAT to route traffic
  2. Internet gateway must be configured as the default route for each public subnet
     • if default route is not configured
       • subnet remains private

Info

• The instance network interface is not configured with this public IP address
  • configured with an IP address for the subnet
• The public address is used by the virtualization management layer only
  • Public IP addresses can be assigned from
    • your own pool
    • from a CSP-managed service
      • e.g., Amazon’s Elastic IP

• Other ways to provision external connectivity for a subnet:
  • NAT gateway
    • allows an instance to connect out to the Internet or to other AWS services
    • does not allow connections initiated from the Internet
  • VPN
    • various options to establish connections
      • using VPNs are software-layer
      • or CSP-managed features

Info

• Internet gateway and a NAT gateway use NAT, but in different ways
  • Internet gateway
    • is a two-way gateway
    • requires the VM to be associated with a public IP address instance
  • NAT gateway
    • is a one-way (outbound only) gateway
    • does not require the VM to be associated with a public IP