Creating a custom VPC in AWS - Visual Walkthrough

Process Flow - Creating a custom VPC

Start

↓

Define VPC CIDR

↓

Create VPC

↓

Create Subnets

↓

Create Internet Gateway

↓

Attach Internet Gateway to VPC

↓

Create Route Table

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Add Route to Internet Gateway

↓

Associate Route Table with Subnets

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End: Custom VPC Ready

The flow shows the steps to create a custom VPC: define IP range, create VPC, add subnets, set up internet gateway, route table, and associate them.

Execution Sample

AWS

aws ec2 create-vpc --cidr-block 10.0.0.0/16
aws ec2 create-subnet --vpc-id vpc-1234 --cidr-block 10.0.1.0/24
aws ec2 create-internet-gateway
aws ec2 attach-internet-gateway --vpc-id vpc-1234 --internet-gateway-id igw-1234
aws ec2 create-route-table --vpc-id vpc-1234
aws ec2 create-route --route-table-id rtb-1234 --destination-cidr-block 0.0.0.0/0 --gateway-id igw-1234
aws ec2 associate-route-table --subnet-id subnet-1234 --route-table-id rtb-1234

This sequence creates a VPC with a subnet, internet gateway, route table, and connects them for internet access.

Process Table

Step	Action	Resource Created/Modified	ID/Value	State After Action
1	Create VPC with CIDR 10.0.0.0/16	VPC	vpc-1234	VPC vpc-1234 created with CIDR 10.0.0.0/16
2	Create Subnet in VPC vpc-1234 with CIDR 10.0.1.0/24	Subnet	subnet-1234	Subnet subnet-1234 created in vpc-1234
3	Create Internet Gateway	Internet Gateway	igw-1234	Internet Gateway igw-1234 created
4	Attach Internet Gateway igw-1234 to VPC vpc-1234	Attachment	igw-1234 attached	Internet Gateway attached to VPC
5	Create Route Table in VPC vpc-1234	Route Table	rtb-1234	Route Table rtb-1234 created
6	Create Route 0.0.0.0/0 via igw-1234 in rtb-1234	Route	route-1	Route to internet added in route table
7	Associate Route Table rtb-1234 with Subnet subnet-1234	Association	assoc-1	Subnet uses route table with internet access
8	End	N/A	N/A	Custom VPC setup complete with internet access

💡 All resources created and connected; VPC is ready for use with internet access.

Status Tracker

Resource	Initial	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	After Step 6	After Step 7	Final
VPC	None	vpc-1234 (CIDR 10.0.0.0/16)	vpc-1234	vpc-1234	vpc-1234	vpc-1234	vpc-1234	vpc-1234	vpc-1234
Subnet	None	None	subnet-1234 (CIDR 10.0.1.0/24)	subnet-1234	subnet-1234	subnet-1234	subnet-1234	subnet-1234 (associated)	subnet-1234 (associated)
Internet Gateway	None	None	None	igw-1234	igw-1234 attached	igw-1234 attached	igw-1234 attached	igw-1234 attached	igw-1234 attached
Route Table	None	None	None	None	rtb-1234	rtb-1234 with route	rtb-1234 with route	rtb-1234 with route	rtb-1234 with route

Key Moments - 3 Insights

Why do we need to attach the Internet Gateway to the VPC after creating it?

Creating the Internet Gateway alone does not connect it to the VPC. Step 4 attaches it, enabling internet traffic routing as shown in execution_table row 4.

What happens if we don't associate the route table with the subnet?

Without association (step 7), the subnet won't use the route table with internet access, so instances can't reach the internet. See execution_table row 7 for association importance.

Why define CIDR blocks when creating VPC and subnet?

CIDR blocks define IP address ranges. The VPC CIDR (step 1) is large, and subnet CIDR (step 2) is a smaller part inside it, ensuring organized IP allocation.

Visual Quiz - 3 Questions

Look at the execution_table at step 3. What resource is created?

A Route Table rtb-1234

B Subnet subnet-1234

C Internet Gateway igw-1234

D VPC vpc-1234

💡 Hint

Check the 'Resource Created/Modified' column at step 3 in execution_table.

At which step does the subnet get associated with the route table?

A Step 7

B Step 6

C Step 5

D Step 4

💡 Hint

Look for 'Associate Route Table' action in execution_table rows.

If the Internet Gateway was not attached to the VPC, what would be the state of internet access?

A Internet access would work normally

B Internet access would fail because IGW is not attached

C Subnet would have internet access without IGW

D Route table would automatically fix it

💡 Hint

Refer to key_moments explanation about attaching IGW and execution_table step 4.

Concept Snapshot

Creating a custom VPC:
- Define a CIDR block (IP range) for the VPC
- Create the VPC resource
- Create subnets inside the VPC with smaller CIDRs
- Create and attach an Internet Gateway for internet access
- Create a route table and add a route to the IGW
- Associate the route table with subnets
- Result: VPC with internet connectivity ready for instances

Full Transcript

To create a custom VPC, start by defining the IP address range using a CIDR block. Then create the VPC resource with this CIDR. Next, create one or more subnets inside the VPC, each with a smaller CIDR block. Create an Internet Gateway and attach it to the VPC to enable internet access. Create a route table for the VPC and add a route that sends all internet traffic (0.0.0.0/0) to the Internet Gateway. Finally, associate this route table with the subnets so that instances inside can use it. This setup allows instances in the subnet to communicate with the internet through the VPC.

Practice

1. What is the main purpose of creating a custom VPC in AWS?

easy

A. To automatically create public IP addresses for all instances

B. To connect your AWS account to social media platforms

C. To enable AWS to manage your network without your input

D. To have a private network with a specific IP range for your resources

Solution

1. Step 1: Understand what a VPC is

   A VPC is a private network in AWS where you control IP ranges and network settings.

2. Step 2: Identify the purpose of a custom VPC

   Creating a custom VPC lets you choose your IP range and control network setup for your resources.

3. Final Answer:

   To have a private network with a specific IP range for your resources -> Option D

4. Quick Check:

   Custom VPC = Private network with chosen IP range [OK]

Hint: Custom VPC means your own private network in AWS [OK]

Common Mistakes:

• Thinking VPC automatically assigns public IPs
• Believing AWS manages the network without user control
• Confusing VPC with external internet connections

2. Which of the following is the correct way to specify the CIDR block when creating a custom VPC?

easy

A. 192.168.1.256/24

B. 255.255.255.0

C. 10.0.0.0/16

D. 10.0.0.0/33

Solution

1. Step 1: Understand CIDR notation

   CIDR block defines IP range with format like x.x.x.x/y where y is between 0 and 32.

2. Step 2: Check each option for validity

   10.0.0.0/16 is valid CIDR (10.0.0.0/16). 255.255.255.0 is a subnet mask, not CIDR. 192.168.1.256/24 has invalid IP (256). 10.0.0.0/33 has invalid prefix length (33).

3. Final Answer:

   10.0.0.0/16 -> Option C

4. Quick Check:

   CIDR block format = x.x.x.x/y with y ≤ 32 [OK]

Hint: CIDR uses / and prefix ≤ 32, IP parts ≤ 255 [OK]

Common Mistakes:

• Using subnet mask instead of CIDR
• Using invalid IP numbers like 256
• Using prefix length greater than 32

3. Given this AWS CLI command to create a VPC:

aws ec2 create-vpc --cidr-block 10.1.0.0/16 --tag-specifications 'ResourceType=vpc,Tags=[{Key=Name,Value=MyVPC}]'

What will be the result?

medium

A. A VPC with CIDR 10.1.0.0/16 and a Name tag 'MyVPC' will be created

B. The command will fail due to incorrect tag syntax

C. A VPC with default CIDR will be created ignoring the specified CIDR

D. A subnet will be created instead of a VPC

Solution

1. Step 1: Analyze the CLI command structure

   The command uses 'create-vpc' with a valid CIDR block and correct tag specification syntax.

2. Step 2: Understand the effect of the command

   This creates a VPC with the given CIDR and applies the Name tag 'MyVPC' to it.

3. Final Answer:

   A VPC with CIDR 10.1.0.0/16 and a Name tag 'MyVPC' will be created -> Option A

4. Quick Check:

   Valid CLI command creates VPC with CIDR and tags [OK]

Hint: Tags use 'ResourceType' and 'Tags' in CLI [OK]

Common Mistakes:

• Incorrect tag syntax causing command failure
• Confusing subnet creation with VPC creation
• Ignoring the CIDR block parameter

4. You created a custom VPC but forgot to enable DNS hostnames. What is the best way to fix this?

medium

A. Modify the VPC attribute to enable DNS hostnames using AWS console or CLI

B. Delete the VPC and create a new one with DNS hostnames enabled

C. Create a new subnet with DNS hostnames enabled

D. DNS hostnames cannot be enabled after VPC creation

Solution

1. Step 1: Understand DNS hostnames setting in VPC

   DNS hostnames is a VPC attribute that can be enabled or disabled after creation.

2. Step 2: Identify how to enable DNS hostnames

   You can modify the VPC attribute via AWS console or CLI without deleting the VPC.

3. Final Answer:

   Modify the VPC attribute to enable DNS hostnames using AWS console or CLI -> Option A

4. Quick Check:

   DNS hostnames can be enabled post-creation [OK]

Hint: VPC attributes can be changed anytime without deletion [OK]

Common Mistakes:

• Thinking you must delete and recreate the VPC
• Trying to enable DNS hostnames on a subnet instead of VPC
• Believing DNS hostnames are enabled by default always

5. You want to create a custom VPC with two public subnets in different availability zones and enable DNS support and hostnames. Which sequence of steps is correct?

hard

A. Attach internet gateway first, then create VPC and subnets, DNS settings are automatic

B. Create VPC with CIDR, enable DNS support and hostnames, create two public subnets in different AZs, attach internet gateway

C. Create VPC with CIDR, create subnets, attach internet gateway, then enable DNS support and hostnames

D. Create two subnets first, then create VPC, enable DNS hostnames, attach internet gateway

Solution

1. Step 1: Create the VPC with chosen CIDR block

   The VPC must exist before creating subnets or attaching gateways.

2. Step 2: Enable DNS support and hostnames on the VPC

   This ensures resources inside can resolve names properly.

3. Step 3: Create two public subnets in different availability zones

   Subnets must be inside the VPC and in separate AZs for high availability.

4. Step 4: Attach an internet gateway to allow internet access

   This makes the subnets public.

5. Final Answer:

   Create VPC with CIDR, enable DNS support and hostnames, create two public subnets in different AZs, attach internet gateway -> Option B

6. Quick Check:

   VPC -> DNS -> Subnets -> Internet Gateway [OK]

Hint: VPC first, then DNS settings, subnets, internet gateway [OK]

Common Mistakes:

• Creating subnets before the VPC exists
• Attaching internet gateway before VPC creation
• Assuming DNS settings are automatic