Default VPC overview in AWS - Mini Project: Build & Apply

Default VPC overview

📖 Scenario: You are starting to learn about AWS networking. Every AWS account has a default Virtual Private Cloud (VPC) that lets you launch resources easily without extra setup.Think of the default VPC as a ready-made neighborhood where your cloud computers can live and talk to each other right away.

🎯 Goal: Build a simple AWS CloudFormation template that defines a default VPC with its main components: subnets, internet gateway, and route table. This will help you understand how a default VPC is structured.

📋 What You'll Learn

Create a VPC resource with the default CIDR block 172.31.0.0/16

Add two public subnets in different availability zones

Attach an Internet Gateway to the VPC

Create a route table with a route to the Internet Gateway

Associate the route table with the public subnets

💡 Why This Matters

🌍 Real World

Default VPCs let you quickly launch cloud resources without manual network setup. Understanding their structure helps you customize your cloud network safely.

💼 Career

Cloud engineers and architects often work with VPCs to design secure and scalable cloud networks. Knowing default VPC components is foundational.

1

Create the VPC resource

Create a resource called DefaultVPC of type AWS::EC2::VPC with the property CidrBlock set to "172.31.0.0/16".

AWS

# Create the DefaultVPC resource here

Hint

The VPC resource needs a CidrBlock property with the value "172.31.0.0/16".

2

Add two public subnets

Add two resources called PublicSubnet1 and PublicSubnet2 of type AWS::EC2::Subnet. Set their VpcId to { Ref: DefaultVPC }. Use CidrBlock values "172.31.0.0/20" and "172.31.16.0/20" respectively. Set AvailabilityZone to "us-east-1a" and "us-east-1b" respectively.

AWS

Resources:
  DefaultVPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: "172.31.0.0/16"

# Add PublicSubnet1 and PublicSubnet2 resources here

Hint

Each subnet needs VpcId, CidrBlock, and AvailabilityZone properties.

3

Add Internet Gateway and Route Table

Add a resource called InternetGateway of type AWS::EC2::InternetGateway. Then add a resource called VPCGatewayAttachment of type AWS::EC2::VPCGatewayAttachment that attaches InternetGateway to DefaultVPC. Next, add a resource called PublicRouteTable of type AWS::EC2::RouteTable with VpcId set to { Ref: DefaultVPC }. Finally, add a resource called PublicRoute of type AWS::EC2::Route with RouteTableId set to { Ref: PublicRouteTable }, DestinationCidrBlock set to "0.0.0.0/0", and GatewayId set to { Ref: InternetGateway }.

AWS

Resources:
  DefaultVPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: "172.31.0.0/16"

  PublicSubnet1:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: { Ref: DefaultVPC }
      CidrBlock: "172.31.0.0/20"
      AvailabilityZone: "us-east-1a"

  PublicSubnet2:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: { Ref: DefaultVPC }
      CidrBlock: "172.31.16.0/20"
      AvailabilityZone: "us-east-1b"

# Add InternetGateway, VPCGatewayAttachment, PublicRouteTable, and PublicRoute resources here

Hint

Remember to attach the Internet Gateway to the VPC and create a route to allow internet traffic.

4

Associate route table with public subnets

Add two resources called SubnetRouteTableAssociation1 and SubnetRouteTableAssociation2 of type AWS::EC2::SubnetRouteTableAssociation. Set their SubnetId to { Ref: PublicSubnet1 } and { Ref: PublicSubnet2 } respectively. Set their RouteTableId to { Ref: PublicRouteTable }.

AWS

Resources:
  DefaultVPC:
    Type: AWS::EC2::VPC
    Properties:
      CidrBlock: "172.31.0.0/16"

  PublicSubnet1:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: { Ref: DefaultVPC }
      CidrBlock: "172.31.0.0/20"
      AvailabilityZone: "us-east-1a"

  PublicSubnet2:
    Type: AWS::EC2::Subnet
    Properties:
      VpcId: { Ref: DefaultVPC }
      CidrBlock: "172.31.16.0/20"
      AvailabilityZone: "us-east-1b"

  InternetGateway:
    Type: AWS::EC2::InternetGateway

  VPCGatewayAttachment:
    Type: AWS::EC2::VPCGatewayAttachment
    Properties:
      VpcId: { Ref: DefaultVPC }
      InternetGatewayId: { Ref: InternetGateway }

  PublicRouteTable:
    Type: AWS::EC2::RouteTable
    Properties:
      VpcId: { Ref: DefaultVPC }

  PublicRoute:
    Type: AWS::EC2::Route
    Properties:
      RouteTableId: { Ref: PublicRouteTable }
      DestinationCidrBlock: "0.0.0.0/0"
      GatewayId: { Ref: InternetGateway }

# Add SubnetRouteTableAssociation1 and SubnetRouteTableAssociation2 resources here

Hint

Each subnet needs to be associated with the public route table to enable internet access.

Practice

1. What is the main purpose of the AWS Default VPC?

easy

A. To monitor application performance

B. To store data backups automatically

C. To provide a ready-to-use network for launching resources quickly

D. To manage user permissions and roles

Solution

1. Step 1: Understand what a VPC is

   A VPC is a virtual network where AWS resources run.

2. Step 2: Identify the role of the Default VPC

   The Default VPC is pre-made to let users launch resources without extra setup.

3. Final Answer:

   To provide a ready-to-use network for launching resources quickly -> Option C

4. Quick Check:

   Default VPC = ready network [OK]

Hint: Default VPC means ready network for quick resource launch [OK]

Common Mistakes:

• Confusing VPC with storage or permissions
• Thinking Default VPC manages backups
• Assuming Default VPC monitors performance

2. Which of the following is TRUE about the Default VPC's subnets?

easy

A. Subnets must be created manually before use

B. It has no subnets by default

C. It only has private subnets without internet access

D. It includes one subnet in each Availability Zone

Solution

1. Step 1: Recall Default VPC subnet setup

   The Default VPC automatically creates one subnet per Availability Zone.

2. Step 2: Check internet access for subnets

   These subnets are public and have internet access by default.

3. Final Answer:

   It includes one subnet in each Availability Zone -> Option D

4. Quick Check:

   Default VPC = subnet per AZ [OK]

Hint: Default VPC auto-creates subnets per AZ [OK]

Common Mistakes:

• Thinking Default VPC has no subnets
• Assuming subnets are private only
• Believing subnets require manual creation

3. If you launch an EC2 instance in the Default VPC, what is the default behavior regarding internet access?

medium

A. The instance automatically gets a public IP and internet access

B. The instance can only access other instances in the same subnet

C. The instance has no internet access unless manually configured

D. The instance is blocked from all network traffic by default

Solution

1. Step 1: Understand Default VPC internet setup

   Default VPC subnets are public and assign public IPs automatically.

2. Step 2: Check instance network behavior

   Instances launched get internet access by default through the internet gateway.

3. Final Answer:

   The instance automatically gets a public IP and internet access -> Option A

4. Quick Check:

   Default VPC instance = public IP + internet [OK]

Hint: Default VPC instances get public IPs automatically [OK]

Common Mistakes:

• Assuming no internet without manual setup
• Thinking instances are isolated by default
• Believing network traffic is blocked initially

4. You try to launch an EC2 instance in the Default VPC but get a network error. What is the most likely cause?

medium

A. The Default VPC was deleted or modified incorrectly

B. You forgot to create a subnet manually

C. The instance type is not supported in the Default VPC

D. AWS does not allow EC2 in Default VPC

Solution

1. Step 1: Recall Default VPC properties

   Default VPC exists by default with subnets and internet gateway.

2. Step 2: Analyze network error cause

   If network errors occur, it often means the Default VPC was deleted or changed wrongly.

3. Final Answer:

   The Default VPC was deleted or modified incorrectly -> Option A

4. Quick Check:

   Network error = Default VPC missing/changed [OK]

Hint: Network errors often mean Default VPC missing or changed [OK]

Common Mistakes:

• Assuming subnets must be created manually
• Thinking instance type blocks launch
• Believing EC2 is disallowed in Default VPC

5. You want to launch a private EC2 instance without internet access using the Default VPC. What should you do?

hard

A. Launch in the Default VPC subnet and disable the public IP

B. Create a new private subnet in the Default VPC and launch the instance there

C. Use the Default VPC as is; all instances are private by default

D. Delete the Default VPC and create a custom VPC with no internet gateway

Solution

1. Step 1: Understand Default VPC subnet types

   Default VPC subnets are public with internet access by default.

2. Step 2: Plan for private instance launch

   To have a private instance, create a new private subnet without internet gateway attachment.

3. Step 3: Avoid deleting Default VPC unnecessarily

   Deleting Default VPC is not required; just add private subnet inside it.

4. Final Answer:

   Create a new private subnet in the Default VPC and launch the instance there -> Option B

5. Quick Check:

   Private instance = new private subnet in Default VPC [OK]

Hint: Add private subnet in Default VPC for no internet [OK]

Common Mistakes:

• Assuming disabling public IP alone makes instance private
• Thinking all Default VPC instances are private
• Deleting Default VPC unnecessarily