Defining custom DNS Servers for VPN clients

Question

Pulumi · Accepted Answer

To define custom DNS servers for VPN clients on AWS, you would typically use an AWS Client VPN Endpoint. The AWS Client VPN allows clients to establish a secure and private connection to a VPC. You can specify custom DNS servers for your VPN to ensure that your clients resolve domain names using the DNS server of your choice.

Here's how you can use Pulumi to create a Client VPN Endpoint with custom DNS servers:

1. We'll start by creating a Client VPN Endpoint using the `aws.ec2clientvpn.Endpoint` resource.
2. You'll need to specify a server certificate ARN and the client CIDR block, as well as other configurations including `dnsServers` for the custom DNS settings.
3. We'll also attach a Network Association with a target subnet using `aws.ec2clientvpn.NetworkAssociation` which allows clients to access resources within the specified subnet.

Below is the TypeScript program that accomplishes these steps:

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

// Create an AWS Client VPN Endpoint with custom DNS servers.
const clientVpnEndpoint = new aws.ec2clientvpn.Endpoint("customDnsVpnEndpoint", {
    // The server certificate ARN is required for the VPN endpoint creation.
    serverCertificateArn: "arn:aws:acm:region:account:certificate/your-certificate-id",
    // Specify the client CIDR block for VPN client IP address allocation.
    clientCidrBlock: "10.0.0.0/16",
    // Define custom DNS servers here. Replace with your own DNS server IPs.
    dnsServers: ["10.0.0.2", "10.0.0.3"],
    description: "Client VPN with custom DNS servers",
    transportProtocol: "udp",
    // Other configurations such as authentication can be added here.
});

// In this example, we're assuming that there's an existing VPC and subnet.
// Replace these with your actual VPC and subnet IDs.
const vpcId = "vpc-12345678";
const subnetId = "subnet-12345678";

// Associate the Client VPN Endpoint with a subnet in the VPC.
const vpnNetworkAssociation = new aws.ec2clientvpn.NetworkAssociation("customDnsVpnNetworkAssoc", {
    clientVpnEndpointId: clientVpnEndpoint.id,
    targetNetworkCidr: "10.0.1.0/24",
    vpcId: vpcId,
    subnetId: subnetId,
});

// Export the VPN endpoint ID
export const vpnEndpointId = clientVpnEndpoint.id;

// In case you need to output the DNS servers configuration.
export const vpnDnsServers = clientVpnEndpoint.dnsServers;
```

### Explanation:

- We use the `aws.ec2clientvpn.Endpoint` resource to create the VPN endpoint. The DNS servers are specified with the `dnsServers` parameter.

- We also define a network association to a VPC and subnet, which is necessary for the VPN to access resources within your AWS environment.

- The `serverCertificateArn` is an ARN to a valid certificate that you must supply, issued by AWS Certificate Manager (ACM). This is necessary for the secure establishment of VPN connections.

After defining the resources, we export the VPN endpoint ID and the DNS configurations for reference or to use in outputs when the Pulumi stack is deployed.

To apply this Pulumi code, save it in a file named `index.ts`, set up your Pulumi stack, and use the Pulumi CLI to deploy it:

```shell
pulumi up
```

This command will provision the AWS Client VPN Endpoint with your custom DNS servers as specified in the Pulumi program. After successful deployment, clients that connect to this VPN will use the custom DNS servers for domain name resolution.