AWS - VPC Gateway - IGW

• Internet gateway (IGWs)

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Internet gateway (IGWs)

• The key: whether it can access internet

• IGW is resilient by design
  • a scalable, redundant, and highly available VPC component
    • horizontally scaled out, redundant, and highly available by default.
  • provide all subnets in all AZs with resilient internet connectivity
• one IGW one VPC
  • Default VPC already has IGW
  • cannot assign more than one IGW to a VPC.

• No network riskdor bandwidth constraints on network traffic.

• allows communication between instances in your VPC and the internet
  • provide a way to get access to the internet
  • allow traffic on the internet to come by providing a target in the subnet route tables

    for internet-routable traffic.

    • Because the instance has a public IP address, the internet can access the public instance with the public IP address.
  • IGW has to add routing rules to the route table for resources in a public subnet to reach the internet

  • rules are not automatically created.

  • IGW two purposes

    :

    • to provide a target in VPC route tables for internet-routable traffic
      • To make subnet public
      • attach an internet gateway
      • add a route to the route table:
        • send non-local traffic through the internet gateway to the internet (0.0.0.0/0).
        • Public IPv4 addresses are never attached to the resource’s network interface.
    • to perform SNAT network address translation for instances that were assigned public IPv4 addresses
      • a record has the mappings of private to public IPs,
      • and the IGW performs SNAT on the associated resource.
        • When the IGW receives a packet from a resource with a public IP
        • it will adjust the packets.
        • It replaces the private IP with the associated public IP address
        • This process is known as SNAT.
• enable access to or from the internet for instances in a VPC subnet, you must ensure:
  • Create an internet gateway
  • Attach an internet gateway to VPC
  • subnet's route table points to the internet gateway
    • Add a route to your subnet’s route table that directs internet-bound traffic to the internet gateway.
  • instances in subnet have public / Elastic IP addresses
    • (public IPv4 address, Elastic IP address, or IPv6 address)
  • NACLs and security groups

    allow the relevant traffic to flow to and from your instance.

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