Adding & Configuring Internet Gateway to AWS VPC | Deep Dive & Hands-On.

Step by step on how to add then Configure an Internet Gateway (IGW) to twtech Custom VPC

Focus:

·       From concept to full routing and traffic flow.

 Breakdown:

•       The Concept: Internet Gateway (IGW)
•       Step-by-Step Process,
•       Step-1, Create or Identify twtech VPC,
•       Step-2, Create an Internet Gateway,
•        Step-3, Attach IGW to the VPC,
•        Step-4, Update the Route Table,
•        Step-5, Configure a Public Subnet,
•        Step-6, Assign Public or Elastic IPs,
•        Step-7, Update Security Groups & NACLs,
•       Traffic Flow Sample,
•       Important Tips.

The Concept: Internet Gateway (IGW)

An Internet Gateway allows resources in the VPC (such as EC2 instances) to:

• Access the Internet (outbound)
• Be accessed from the Internet (inbound)

NB:

Internet Gateway acts as the bridge between twtech VPC and the public Internet.

 Step-by-Step Process

Step-2, Create or Identify Your VPC

If twtech already has a VPC, note its VPC ID,  Otherwise, create one:

# bash 

aws ec2 create-vpc --cidr-block 10.0.0.0/16

Step-2, Create an Internet Gateway

# bash 

aws ec2 create-internet-gateway

Output example:

# json

{

  "InternetGateway": {

    "InternetGatewayId": "igw-0abcd1234efgh5678",

    "Attachments": [ ]

  }

}

Step-3, Attach IGW to the VPC

Attach the IGW to your target VPC:

# bash

aws ec2 attach-internet-gateway \

  --vpc-id vpc-0abcd1234efgh5678 \

  --internet-gateway-id igw-0abcd1234efgh5678

✅   This establishes connectivity between the VPC and the Internet Gateway.

Step-4, Update the Route Table

Add a default route that sends non-local traffic (0.0.0.0/0) to the Internet Gateway.

Example:

# bash

aws ec2 create-route \

  --route-table-id rtb-0123456789abcdef0 \

  --destination-cidr-block 0.0.0.0/0 \

  --gateway-id igw-0abcd1234efgh5678

NB:

 This route tells instances in the public subnet to send Internet-bound traffic to the IGW.

Step-5, Configure a Public Subnet

NB:

A subnet becomes public when its route table includes a route to the IGW.

Example:

• Subnet CIDR: 10.0.1.0/24
• Route Table entry: 0.0.0.0/0 → igw-xxxxxx

✅    Public subnet = Connected to Internet Gateway
❌    Private subnet = Connected to NAT Gateway (or no external route)

Step-6, Assign Public or Elastic IPs

For EC2 instances to communicate with the Internet:

• Auto-assign a public IP on launch, OR
• Associate an Elastic IP (EIP) afterward

NB:

 Without a public IP, even a public subnet instance cannot access the Internet directly.

Step-7, Update Security Groups & NACLs

• Security Group (SG):
• Allow outbound: 0.0.0.0/0
• Allow inbound (for example): SSH (22), HTTP (80), HTTPS (443)
• Network ACL (NACL):
• Inbound: allow ephemeral & specific ports
• Outbound: allow responses to Internet traffic

 Traffic Flow Sample

Outbound (EC2 → Internet):

Inbound (Internet → EC2):

 Important Tips

Feature	Description
One IGW per VPC	A VPC can only have one attached IGW
Free of charge	No cost for IGW; you pay only for data transfer
Highly available	AWS automatically replicates it across AZs
Works with IPv4 & IPv6	IPv6 doesn’t need NAT — uses IGW directly

Example Architecture

Project: Hands-On

How twtech adds then configure the internet Gateway to access resources in its VPC

Search for AWS service:  VPC

Step-1,

• twtech launch an EC2 instances into a custom VPC (twtechvpc). To verify that it has no internet access:

Launch instance:

Edit Network settings:

• Select the custom VPC (twtechvpc) and PublicSubnetA (initially created)

Step-2:

•        Edit the Public Subnet (twtechPublicSubnetA)  from console to: Enable auto Assign IPv4 address.
•        Select and click open the Public Subnet (twtechPublicSubnetA) to enable.

From Action: edit the Subnet settings.

From: Unchecked (Disabled)

Auto-assign IP settings:

• Enable AWS to automatically assign a public IPv4 or IPv6 address to a new primary network interface for an instance in this subnet.

To: checked (enabled)

• Save changes to subnet settings:

Step-3:

•        Also Edit the Public Subnet (twtechPublicSubnetB)  from console to: Enable auto Assign IPv4 address.
•        Select and click open the Public Subnet (twtechPublicSubnetB) to enable.

From: Unchecked (Disabled)

Auto-assign IP settings

• Enable AWS to automatically assign a public IPv4 or IPv6 address to a new primary network interface for an instance in this subnet.

To: checked (enabled)

Save changes to subnet settings:

Step-4:

Return to EC2 instance console and complete network settings:

•        The auto-assign public IP should now be available for enable as well. 
•        If not refresh the page and restart steps in provisioning an ec2 in the custom vpc (twtechvpc)

Firewall (security groups):

• A security group is a set of firewall rules that control the traffic for twtech instance (twtechwebserver). Add rules to allow specific traffic to reach the instance.

Launch instance:

• Verify, then make sure the instance provisioned (twtechwebserver) is running and fully initialized:

• Select instance to see details: below it seen that the instance has been auto assigned a Public IPv4 address.

NB:

• The server has an IPV4 address but does not yet have public intern access (connectivity)

Step-5

• First, Let’s verify whether the instance has internet connection via: instance connect

• Console output: error establishing connection to instance.

Step-6:

• How twtech adds internet connectivity via IGW (to allow public access) into the public subnets of its custom vpc created (twtechVPC).

Return to VPC console to add internet Gateway (IGW): to the Public subnets

• Create an Internet Gateway:

Create internet gateway

• An internet gateway is a virtual router that connects a VPC to the internet. To create a new internet gateway specify the name for the gateway below.

• Create internet gateway:

Step-7:

• Attach the internet Gateway (twtecgIGW) to the VPC (twtechvpc)

• Seletec the VPC (twtechvpc) and attach the IGW (twtechIGW)

Step-8,

• Verify again if the VPC (twtechvpc) now has internet:  using EC2 instance connect from EC2 console

• There is still a problem connection to instance: How to get that fixed.

• Even though twtech now has internet gateway in its VPC, it needs yet to be assigned a: Route table.

Step-9:

• Edit or create a special route table (rt) to: associate with the IGW

• Create route table: twtechPublicRT

• Create another route table: twtechPrivateRT

Step-10:

•        Assign the subnets to the right route tables: Public subnets to public route (subnet Association)
•        Select the route table to be associated, then click on Subnet association tab (below) and: edit subnet association.

Add all the Public subnets in the Public Route table

• Edit subnet associations
• Change which subnets are associated with this route table.

Again:

• Assign the subnets to the right route tables: Private subnets to Private route table.

• Both the public and private route tables have 2 subnets associated with them.

Step-11:

• Edit routes in the Public route table to add internet connect (Public access) to exist local access (within the vpc)

From: local connection within the VPC only

To: Add route for public internet

Save edited routes:

Step-12: Finally

• Verify again if the VPC (twtechvpc) now has internet:  using EC2 instance connect from EC2 console

Successfully,

•        twtech has created a: custom VPC, subnets (private/public), Internet gateway (IGW) and associate with subnets, edited Public route table to add internet that is associated with the Public subnet.
•        twtech also successfully connected into the instances created in its public subnet.
•        All twtech resources provision in the public subnet of the custom vpc (twtechvpc) are now accessible from the Public internet.

Trying to ping some accounts:

ping think-with-tech.blogspot.com

twtechVPC Layout: