Static and Dynamic IP Addresses - Internet Protocols

Task 1: Investigating the Customer's Environment

I began by recalling what I've learned about static and dynamic IP addresses. Based on Bob's description that his EC2 instance's IP changes every time he stops and starts it again, I suspected he was using a dynamic IP address. To test this theory, I decided to launch an EC2 instance in the AWS environment to replicate and troubleshoot the issue.

In the scenario, Bob was having issues with his EC2 instance constantly changing IP addresses every time he stopped and started his instance. He couldn't leave his instance running because it was very expensive, and he required a static IP address to prevent breaking other resources attached to it.

Creating an EC2 Instance to Test

I navigated to the Amazon EC2 dashboard and followed these steps to create a new instance:

1. Choose an Amazon Machine Image (AMI):
   • I selected the first entry for Amazon Linux 2 AMI (HVM)
   • This AMI provided the OS and configuration template for the EC2 instance
2. Choose an Instance Type:
   • I selected t3.micro
   • Then navigated to the bottom of the window and clicked "Next: Configure Instance Details"
3. Configure Instance Details:
   • Network: I chose vpc-xxxxxxxx | Lab VPC
   • Subnet: I chose subnet-xxxxxx | Public Subnet 1
   • Auto-assign Public IP: I set this to enable
   • I left everything else as default and selected "Next: Add Storage"
4. Add Storage:
   • I left this as default
   • Selected "Next: Add Tags"
5. Add Tags:
   • I clicked "Add Tag"
   • Under Key, I entered "Name"
   • Under Value, I entered "test instance"
   • Then selected "Next: Configure Security Group"
6. Configure Security Group:
   • Under "Assign a security group", I selected the "Select an existing security group" radio button
   • I chose the security group named "Linux Instance SG"
   • Then clicked "Review and Launch"
7. Review Instance Launch:
   • I clicked "Launch"
   • In the key pair pop-up window, I kept "Choose an existing key pair" in the first dropdown
   • In the second dropdown, I selected the key pair "vockey | RSA"
   • I checked the acknowledgment box
   • Finally, I clicked "Launch Instances"

Testing IP Address Behavior

Once my instance was created, I waited until the status changed to "2/2" before continuing. I selected the checkbox of my test instance and viewed the Networking tab at the bottom of the screen. Here, I observed and noted both the Public IPv4 address and the Private IPv4 address.

To test the IP address behavior, I performed the following steps:

1. I selected the "Instance state" dropdown button and chose "Stop instance"
2. Once the status changed to "Stopped", I observed the Public and Private IPv4 addresses
3. I noticed the Public IPv4 address was no longer present
4. I restarted the instance by selecting "Instance state" and "Start instance"
5. After the status changed to "Running", I observed both addresses again

I noticed that when I stopped and started the EC2 instance, the Public IPv4 address changed to a completely new IP address, while the Private IPv4 address remained the same. This confirmed that the Public IP was indeed a dynamic IP address, while the Private IP was static within the VPC.

This test successfully replicated the exact issue Bob was experiencing - the public IP address changed every time the instance was stopped and started again.

Implementing a Solution: Elastic IP Address

Now that I had confirmed the issue, I needed to implement a solution. Bob needed a permanent Public IP address that wouldn't change when he stopped and restarted his instance. AWS offers a solution called Elastic IP (EIP) specifically for this purpose.

1. From the EC2 dashboard, I navigated to "Network and Security" on the left navigation menu
2. I selected "Elastic IPs"
3. I noticed there were no EIPs already allocated
4. I clicked the "Allocate Elastic IP address" button in the top right
5. I kept all settings as default and clicked "Allocate"
6. I made note of the new EIP address that was created

Next, I needed to associate this EIP with my EC2 instance:

1. I selected the checkbox for the newly created EIP
2. I clicked "Actions" and selected "Associate Elastic IP address"
3. I left the resource type as "Instance"
4. From the "Choose an Instance" dropdown, I selected my "test instance"
5. Under "Private IP address", I selected the empty box and the associated Private IP was automatically selected
6. I clicked the "Associate" button to complete the process

To verify the solution was working correctly:

1. I navigated back to the Instances page
2. I selected my "test instance" and viewed the Networking tab
3. I confirmed that the Public IPv4 address was now the same as my allocated EIP
4. I stopped and started the instance again
5. After it restarted, I checked the Public IPv4 address again

I observed that even after stopping and starting the instance, the Public IPv4 address remained the same - it was now a static IP address thanks to the EIP allocation. This successfully solved the issue that Bob was experiencing!

Summary of Findings

Through my investigation, I discovered that:

• By default, EC2 instances are assigned dynamic public IP addresses that change when instances are stopped and started
• Private IP addresses within a VPC remain static, even when instances are stopped and started
• For applications requiring a persistent public IP address, an Elastic IP (EIP) is the appropriate AWS solution
• Once an EIP is allocated and associated with an instance, the public IP address remains constant regardless of instance state changes

My recommendation to Bob would be to:

1. Allocate an Elastic IP address for his Public Instance
2. Associate the EIP with the instance
3. Update any related resources or configurations to use this new static IP address

This solution allows Bob to stop and start his instance as needed to save costs while maintaining a consistent public IP address for his applications.