Internet Gateway for public access in AWS - Step-by-Step Execution

Process Flow - Internet Gateway for public access

Create VPC

↓

Create Internet Gateway

↓

Attach Internet Gateway to VPC

↓

Create Public Subnet in VPC

↓

Update Route Table

↓

Add Route: 0.0.0.0/0 -> Internet Gateway

↓

Launch Public Resources

↓

Resources have public internet access

This flow shows how to create and attach an Internet Gateway to a VPC, then update routing so public subnet resources can access the internet.

Execution Sample

AWS

resource "aws_vpc" "main" {
  cidr_block = "10.0.0.0/16"
}

resource "aws_internet_gateway" "gw" {
  vpc_id = aws_vpc.main.id
}

resource "aws_route_table" "public" {
  vpc_id = aws_vpc.main.id

  route {
    cidr_block = "0.0.0.0/0"
    gateway_id = aws_internet_gateway.gw.id
  }
}

This code creates a VPC, an Internet Gateway attached to it, and a route table with a route sending all internet traffic to the gateway.

Process Table

Step	Action	Resource Created/Updated	State Change	Result
1	Create VPC	aws_vpc.main	VPC with CIDR 10.0.0.0/16 created	VPC ready
2	Create Internet Gateway	aws_internet_gateway.gw	IGW created but not attached	IGW exists
3	Attach IGW to VPC	aws_internet_gateway.gw	IGW attached to VPC	VPC has IGW
4	Create Route Table	aws_route_table.public	Route table created for VPC	Route table ready
5	Add Route 0.0.0.0/0 -> IGW	aws_route_table.public	Route added to send all traffic to IGW	Public route active
6	Associate Route Table with Subnet	aws_route_table_association.public_assoc	Subnet uses public route table	Subnet routes internet traffic
7	Launch Public Resources	EC2 instances in public subnet	Resources get public IP and route	Resources have internet access
8	End	-	-	Internet Gateway setup complete

💡 All steps complete, public subnet resources can access the internet via the Internet Gateway

Status Tracker

Variable	Start	After Step 1	After Step 3	After Step 5	After Step 7	Final
VPC	None	Created with CIDR 10.0.0.0/16	Attached IGW	Route table created	Subnet associated	Ready with IGW and routes
Internet Gateway	None	Created	Attached to VPC	Route added to route table	Used by subnet	Active for internet access
Route Table	None	None	Created	Route 0.0.0.0/0 -> IGW added	Associated with subnet	Routes internet traffic
Subnet	None	None	None	None	Created and associated	Public subnet with internet access

Key Moments - 3 Insights

Why do we need to attach the Internet Gateway to the VPC?

Attaching the Internet Gateway to the VPC (Step 3) connects the VPC to the internet. Without this, the gateway exists but cannot route traffic for the VPC, so public access won't work.

What happens if we don't add the route 0.0.0.0/0 to the Internet Gateway?

Without the route (Step 5), the subnet's traffic won't know to use the Internet Gateway to reach the internet. So even if the gateway is attached, resources won't have internet access.

Why associate the route table with the subnet?

Associating the route table with the subnet (Step 6) tells the subnet to use the routes defined, including the internet route. Without this, the subnet uses the default route table which may not have internet access.

Visual Quiz - 3 Questions

Look at the execution table, at which step is the Internet Gateway attached to the VPC?

A Step 2

B Step 5

C Step 3

D Step 6

💡 Hint

Check the 'Action' and 'State Change' columns in the execution table rows.

According to the variable tracker, what is the state of the Route Table after Step 5?

A Route 0.0.0.0/0 -> IGW added

B Route table created with no routes

C Route table associated with subnet

D Route table deleted

💡 Hint

Look at the 'Route Table' row under 'After Step 5' in the variable tracker.

If the route 0.0.0.0/0 -> IGW was missing, what would be the result?

A Internet Gateway would not be created

B Subnet traffic would not reach the internet

C Resources still have internet access

D VPC would be deleted

💡 Hint

Refer to the key moment about the importance of the route in the execution table step 5.

Concept Snapshot

Internet Gateway connects a VPC to the internet.
Create IGW, attach to VPC.
Add route 0.0.0.0/0 in route table pointing to IGW.
Associate route table with public subnet.
Resources in subnet get internet access.

Full Transcript

This visual execution shows how to set up an Internet Gateway for public access in AWS. First, a VPC is created with a CIDR block. Then an Internet Gateway is created and attached to the VPC. A route table is created and a route is added to send all internet traffic (0.0.0.0/0) to the Internet Gateway. This route table is associated with a public subnet. Finally, resources launched in this subnet receive public IPs and can access the internet through the Internet Gateway. Key points include attaching the gateway to the VPC, adding the correct route, and associating the route table with the subnet to enable internet access.

Practice

1. What is the main purpose of an Internet Gateway in AWS?

easy

A. To allow communication between a VPC and the internet

B. To store data securely in the cloud

C. To manage user permissions in AWS

D. To create private subnets within a VPC

Solution

1. Step 1: Understand the role of an Internet Gateway

   An Internet Gateway is a component that connects a Virtual Private Cloud (VPC) to the internet, enabling resources in the VPC to access or be accessed from the internet.

2. Step 2: Identify the correct purpose

   Among the options, only allowing communication between a VPC and the internet matches the Internet Gateway's function.

3. Final Answer:

   To allow communication between a VPC and the internet -> Option A

4. Quick Check:

   Internet Gateway = Connects VPC to internet [OK]

Hint: Internet Gateway connects VPC to internet, not storage or permissions [OK]

Common Mistakes:

• Confusing Internet Gateway with storage services
• Thinking it manages user permissions
• Assuming it creates private subnets

2. Which AWS resource must an Internet Gateway be attached to for it to provide internet access?

easy

A. An EC2 instance

B. A Virtual Private Cloud (VPC)

C. An S3 bucket

D. A Security Group

Solution

1. Step 1: Identify the attachment requirement of an Internet Gateway

   An Internet Gateway must be attached to a VPC to enable internet access for resources inside that VPC.

2. Step 2: Match the correct AWS resource

   Among the options, only a VPC is the correct resource to attach an Internet Gateway to.

3. Final Answer:

   A Virtual Private Cloud (VPC) -> Option B

4. Quick Check:

   Internet Gateway attaches to VPC [OK]

Hint: Internet Gateway attaches only to VPC, not instances or buckets [OK]

Common Mistakes:

• Trying to attach Internet Gateway directly to EC2
• Confusing with storage like S3 buckets
• Thinking it attaches to Security Groups

3. Given the following AWS setup, what will happen if the Internet Gateway is not attached to the VPC?

VPC: vpc-1234
Internet Gateway: igw-5678 (created but not attached)
EC2 Instance: in public subnet with route to igw-5678

medium

A. The EC2 instance will not have internet access

B. The EC2 instance will be terminated automatically

C. The EC2 instance will have internet access

D. The EC2 instance will have internet access only for outbound traffic

Solution

1. Step 1: Understand Internet Gateway attachment requirement

   An Internet Gateway must be attached to the VPC to enable internet traffic flow. Without attachment, the gateway is inactive for that VPC.

2. Step 2: Analyze the effect on EC2 instance

   Even if the route table points to the Internet Gateway, since it is not attached, the EC2 instance cannot send or receive internet traffic.

3. Final Answer:

   The EC2 instance will not have internet access -> Option A

4. Quick Check:

   Internet Gateway unattached = no internet access [OK]

Hint: Internet Gateway must be attached to VPC for internet access [OK]

Common Mistakes:

• Assuming route table alone enables internet
• Thinking instance auto-terminates without internet
• Believing outbound-only access works without attachment

4. You created an Internet Gateway and attached it to your VPC, but your EC2 instance in the public subnet still cannot access the internet. What is the most likely cause?

medium

A. The Internet Gateway is not attached to the VPC

B. The EC2 instance is stopped

C. The route table for the subnet does not have a route to the Internet Gateway

D. The security group allows all traffic

Solution

1. Step 1: Confirm Internet Gateway attachment

   The question states the Internet Gateway is attached to the VPC, so this is not the issue.

2. Step 2: Check route table configuration

   For internet access, the subnet's route table must have a route directing 0.0.0.0/0 traffic to the Internet Gateway. Missing this route blocks internet access.

3. Final Answer:

   The route table for the subnet does not have a route to the Internet Gateway -> Option C

4. Quick Check:

   Route table missing IGW route = no internet [OK]

Hint: Check route table for 0.0.0.0/0 route to IGW [OK]

Common Mistakes:

• Ignoring route table routes
• Assuming attachment alone grants internet
• Confusing security group rules with routing

5. You want to provide internet access to instances in a public subnet of your VPC. Which combination of steps is required to achieve this?

hard

A. Create a VPN connection and update the route table to route 0.0.0.0/0 to the VPN

B. Create a NAT Gateway, attach it to the VPC, and assign private IPs to instances

C. Attach an Internet Gateway to the subnet directly and assign Elastic IPs to instances

D. Create and attach an Internet Gateway to the VPC, update the subnet's route table to route 0.0.0.0/0 to the Internet Gateway, and ensure instances have public IPs

Solution

1. Step 1: Attach Internet Gateway to VPC

   Internet Gateway must be created and attached to the VPC to enable internet connectivity.

2. Step 2: Update subnet route table

   The route table for the public subnet must have a route sending all internet-bound traffic (0.0.0.0/0) to the Internet Gateway.

3. Step 3: Assign public IPs to instances

   Instances need public IP addresses to communicate over the internet directly.

4. Final Answer:

   Create and attach an Internet Gateway to the VPC, update the subnet's route table to route 0.0.0.0/0 to the Internet Gateway, and ensure instances have public IPs -> Option D

5. Quick Check:

   IGW + route + public IP = internet access [OK]

Hint: Internet Gateway + route + public IP = public internet access [OK]

Common Mistakes:

• Confusing NAT Gateway with Internet Gateway for public subnet
• Trying to attach IGW to subnet directly
• Forgetting to assign public IPs to instances