Internet Gateway for public access in AWS - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Architecture

intermediate

Identify the correct Internet Gateway attachment

You have a Virtual Private Cloud (VPC) and want to allow public internet access to instances in a public subnet. Which option correctly attaches an Internet Gateway to the VPC?

A Attach the Internet Gateway to the VPC using its ID, then update the route table to direct 0.0.0.0/0 traffic to the Internet Gateway.

B Attach the Internet Gateway to the subnet directly, then update the subnet's route table to direct 0.0.0.0/0 traffic to the Internet Gateway.

C Attach the Internet Gateway to the VPC, but no need to update any route tables for public access.

D Attach the Internet Gateway to the VPC and create a NAT Gateway in the same subnet for public access.

💡 Hint

Remember, Internet Gateways attach to VPCs, not subnets. Public access requires routing traffic through the Internet Gateway.

Internet Gateways must be attached to the VPC. Then, the route table for the public subnet must have a route directing all internet-bound traffic (0.0.0.0/0) to the Internet Gateway. Attaching to subnets or skipping route updates will not enable internet access.

❓ security

intermediate

Security group configuration for public internet access

You have attached an Internet Gateway and updated the route table for a public subnet. What security group rule is required to allow inbound HTTP traffic from the internet to an EC2 instance?

A Allow inbound UDP traffic on port 80 from source 0.0.0.0/0.

B Allow inbound TCP traffic on port 22 from source 0.0.0.0/0.

C Allow outbound TCP traffic on port 80 to source 0.0.0.0/0.

D Allow inbound TCP traffic on port 80 from source 0.0.0.0/0.

💡 Hint

HTTP uses TCP port 80 and inbound traffic must be allowed from anywhere for public access.

To allow public HTTP access, the security group must allow inbound TCP traffic on port 80 from all IP addresses (0.0.0.0/0). Port 22 is for SSH, outbound rules do not control inbound access, and UDP is not used for HTTP.

❓ service_behavior

advanced

Effect of missing Internet Gateway on public subnet traffic

You have a subnet with a route table directing 0.0.0.0/0 traffic to an Internet Gateway, but the Internet Gateway is not attached to the VPC. What will happen when an instance in this subnet tries to access the internet?

A The instance will access the internet normally because the route table has the correct route.

B The instance will fail to reach the internet because the Internet Gateway is not attached to the VPC.

C The instance will access the internet only for outbound traffic but not receive inbound traffic.

D The instance will use the NAT Gateway automatically to reach the internet.

💡 Hint

Routes to an Internet Gateway require the gateway to be attached to the VPC to function.

Even if the route table points to an Internet Gateway, if the gateway is not attached to the VPC, traffic cannot flow through it. This prevents internet access.

❓ Configuration

advanced

Correct Terraform configuration for Internet Gateway attachment

Which Terraform snippet correctly creates and attaches an Internet Gateway to a VPC named 'main-vpc'?

A

resource "aws_internet_gateway" "gw" {
  vpc_id = "main-vpc"
}

B

resource "aws_internet_gateway" "gw" {
  vpc = aws_vpc.main-vpc.id
}

C

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

D

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

💡 Hint

Terraform resource attributes are case-sensitive and must match resource names exactly.

The correct attribute is 'vpc_id' with the exact resource name 'aws_vpc.main_vpc.id'. Using dashes in resource names is invalid in Terraform identifiers.

✅ Best Practice

expert

Best practice for high availability of Internet Gateway in multi-AZ VPC

You have a VPC spanning multiple Availability Zones (AZs). What is the best practice to ensure high availability of internet access for public subnets in all AZs?

A Create one Internet Gateway attached to the VPC; it automatically provides internet access to all AZs.

B Attach the Internet Gateway to each subnet individually to ensure availability.

C Create a NAT Gateway in each AZ instead of an Internet Gateway for public internet access.

D Create one Internet Gateway per AZ and attach each to the VPC for redundancy.

💡 Hint

Internet Gateways are regional and attached to the VPC, not per AZ or subnet.

An Internet Gateway is a horizontally scaled, redundant, and highly available component that attaches to the VPC. One Internet Gateway serves all AZs in the VPC. Creating multiple Internet Gateways or attaching them to subnets is not supported.

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