Aws NAT Instance & NAT Gateway

• Lets create a vpc with 4 subnets
  • web and mgmt public
  • app & db private
• Create one ec2 instance in public subnet (web) and check the whether you are able to access internet
  • From ec2 instance in web subnet we are able to ping internet
• Create one ec2 instance in private subnet (app) and check the whether you are able to access internet (use web ec2 instance as bastion host)
  • ec2 instance in private subnet is unable to connect to internet
• In many cases we would not want machines in private subnet connected from internet but we would want these machine to connect to internet.
• How can i enable internet to machines in private subnet without making them public?
• To understand this lets understand our home internet connection.
• So in AWS, if we can create NAT Server as mentioned in the above image, machines in private subnet can connect to internet. AWS gives us two options
  • NAT-instance:
    • Create an ec2 instance with NAT software in it
    • Assign static public ip address (Elastic IP Address)
    • Change the Route table rules of private router to forward 0.0.0.0/0 to NAT-instance
    • Disadvantages:
      • Since we are creating ec2 instance, os maintenance should be managed by us
      • If this server fails troubleshooting or recreating is our responsibility
  • NAT-gateway
    • NAT as a service
    • AWS will create and manage NAT.
    • We just need to manage routes in our private router.
• Now lets create a NAT gateway in our public subnet and modify the private route table routes
• Now lets verify if the machine in private subnet is able to connect to internet or not
• Note: Nat Gateway is chargable, so delete nat-gateway and release elastic ip address

Multi-Network Scenarios

• Scenario 1: Both Networks in AWS
  • Lets assume we have a web server in a vpc and app server in a different vpc
  • For the application to work web server should communicate with app server.
  • We don’t public connectivity b/w app and web server. How can we establish private connectivity b/w two servers in two different vpc’s
  • Solution: VPC Peering Connection
• Scenario 2: One Network on premise and VPC
  • Your application has a database which is on-premise
  • Webserver is running in AWS VPC, How can i establish a private connectivity b/w webserver and app server
  • Solution: AWS VPN Connections (Point to site and Site to Site)/Direct Connect

What is a Virtual Private Network (VPN)?