README.MD

EC2 DNS Updater

This AWS lambda function will update the DNS records for a given subdomain (defined in the Subdomain tag on an EC2 server) to point to the public IP address of an EC2 instance.

Setup

1. Create a AWS lambda function
2. Set the runtime to Node.js 20.x
3. Set the env variables CF_ZONE_ID and CLOUDFLARE_API_TOKEN
4. Create an EventBridge rule that triggers the lambda function on EC2 instance state change (see below)
5. Run pnpm install on this repo to install the dependencies
6. run pnpm build to build the lambda function
7. Run pnpm deploy to deploy the lambda function to AWS (assuming your lambda function is named DNS_Updater. Make sure you are logged into the aws CLI.)

EventBridge Rule

CloudFormation template

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Description": "CloudFormation template for EventBridge RuleDNSUpdater_Instance_Start",
  "Resources": {
    "Rule0a21bc73": {
      "Type": "AWS::Events::Rule",
      "Properties": {
        "Name": "DNSUpdater_Instance_Start",
        "EventPattern": "{\"source\":[\"aws.ec2\"],\"detail-type\":[\"EC2 Instance State-change Notification\"],\"detail\":{\"state\":[\"running\"]}}",
        "State": "ENABLED",
        "EventBusName": "default",
        "Targets": [{
          "Id": "Id0a53661e-f906-481a-a0e5-ddb594a44468",
          "Arn": {
            "Fn::Sub": "arn:${AWS::Partition}:lambda:${AWS::Region}:${AWS::AccountId}:function:DNS_Updater"
          }
        }]
      }
    }
  },
  "Parameters": {}
}

Event pattern

{
  "source": ["aws.ec2"],
  "detail-type": ["EC2 Instance State-change Notification"],
  "detail": {
    "state": ["running"]
  }
}