Associating Elastic IPs through an Internet Gateway

Question

Pulumi · Accepted Answer

To associate Elastic IPs (EIPs) with an instance in the cloud, you need to allocate the EIP, then assign it to an already running instance or network interface. In AWS, an EIP is a static, public IP address that you can allocate to your account and which can be programmatically remapped to another instance. An Internet Gateway, on the other hand, allows resources like EC2 instances within your VPC to access the internet, and it's required for EIPs to communicate with the internet.

Below, I will provide you with a TypeScript program using Pulumi to create an Elastic IP, an EC2 instance, and an Internet Gateway. For the sake of simplicity, this TypeScript program will assume that you already have a VPC and a subnet created.

In Pulumi, to create an Elastic IP, we'll use the `aws.ec2.Eip` resource. For the internet gateway, we'll use the `aws.ec2.InternetGateway` resource, and to associate the internet gateway with the VPC, we'll utilize the `aws.ec2.VpcAttachment` resource. We will also create an EC2 instance using the `aws.ec2.Instance` resource.

Before you begin, ensure that you have AWS credentials configured for Pulumi.

Here's the TypeScript program:

```typescript
import * as aws from '@pulumi/aws';

// Create an Elastic IP
const elasticIp = new aws.ec2.Eip('myElasticIp', {});

// Provision an Internet Gateway and attach it to your VPC (replace vpcId with your existing VPC ID)
const internetGateway = new aws.ec2.InternetGateway('myInternetGateway', {
    vpcId: 'vpc-12345678', // Replace with your VPC ID
});

// Create an EC2 instance
const instance = new aws.ec2.Instance('myInstance', {
    ami: 'ami-0c55b159cbfafe1f0', // Replace with a valid AMI for your region
    instanceType: 't2.micro',
    subnetId: 'subnet-12345678', // Replace with your Subnet ID
    associatePublicIpAddress: true, // This is set so the instance gets a public IP from the subnet
});

// Associate Elastic IP with the EC2 Instance
const eipAssociation = new aws.ec2.EipAssociation('eipAssoc', {
    instanceId: instance.id,
    allocationId: elasticIp.id,
});

// Export the Elastic IP and the EC2 Instance public DNS
export const elasticIpAddress = elasticIp.publicIp;
export const instancePublicDns = instance.publicDns;
```

In this program:

- We provisioned an Elastic IP (`aws.ec2.Eip`) that will allow the EC2 instance to have a static public IP address that doesn't change across stops/starts.
- We created an Internet Gateway (`aws.ec2.InternetGateway`). This is attached to our specified VPC (you'll replace 'vpc-12345678' with your VPC ID) to enable communication between the instances in the VPC and the internet.
- We launched an EC2 instance within a specified VPC and subnet, which gets a public IP address from the subnet. Please replace 'ami-0c55b159cbfafe1f0' with an appropriate AMI ID for your region and 'subnet-12345678' with your subnet ID.
- We created an EIP association (`aws.ec2.EipAssociation`) between the Elastic IP and our EC2 instance. This ties the static public IP address to our instance.
- We are exporting the Elastic IP address and the EC2 Instance's public DNS name so we can easily access these outputs after deployment.

You can run this Pulumi program by saving the code in a file named `index.ts`, then running `pulumi up` in your terminal within the same directory. Ensure that Pulumi CLI is installed and configured for use with your AWS account.