Can we add a CNAME for an EC2 in Cloud Formation Template when ec2s are created using auto scaling?

user_4763333 0
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I am working with a kafka cluster on AWS, I would like to give each broker a CNAME so I can reference that rather than the IP address.

I know usually with an EC2 we can do this in the cloud formation template using something like this.. 

{
"Parameters": {
    "TestCname":{
        "Description": "The IpAddress for the MyInstance Ec2",
        "Type": "String",
        "Default": "domainName.com"            
    }
},
"Resources": {
    "MyInstanceCNAME": {
        "Type": "Custom::ResourceDNS",
          "Version": "1.0",
          "Properties": {                                            
            "ServiceToken": { "Fn::Sub": "arn:aws:sns:${AWS::Region}:<Account_Num>:custom-resource" },
            "Resource": "CNAME",
            "CNAME": { "Ref": "TestCname" },
            "IpAddress" : { "Fn::GetAtt" : [ "MyInstance", "PrivateIp" ]}
        }
    },
    "MyInstance": {
        "Type": "AWS::EC2::Instance",
        "Properties": {
            "AvailabilityZone": "us-east-1a",
            "ImageId": "ami-a4c7edb2",
            "InstanceType": "t2.micro"}
    }
}

The problem is that with confluent quickstart script for AWS

https://github.com/aws-quickstart/quickstart-confluent-kafka/blob/master/templates/confluent-kafka.template

I initially thought the creation of the ec2s must be in the referenced templates eg. 

Fn::Sub": "https://${QSS3BucketName}.s3.amazonaws.com/${QSS3KeyPrefix}templates/nodegroup.template

But I couldn't see the instantation in that template either and have just discovered through a guy on my team that the ec2s are being created through auto scaling.

Can we add a CNAME and how is the question? Thanks

amazon-cloudformation confluent-platform apache-kafka amazon-web-services amazon-ec2
3 Answers

EC2 Autoscaling helps you setup scaling for your EC2 quickly. The EC2s controlled by this can be terminated or started depending on demand or schedules. Because of this, it does not make sense to reference to any particular EC2.

I would like to suggest two alternatives:

  1. Using an AWS Elastic Load Balancer per group of EC2, each load balancer comes with its own domain but you can assign a custom one if you want. Reference the ELB domain afterwords.
  2. Using an AWS Elastic Beanstalk per group of EC2, this will manage whats underneath for you including the AutoScaling group, Load balancer, EC2, etc. Again, you will have a domain out of the box and you can set your own custom domain. Reference the ELB domain afterwords.

Here is a small cloudformation snippet of how I assign a custom domain name to my ELB:

Resources:
  MyAppEnvironment:
    Type: AWS::ElasticBeanstalk::Environment
    Properties:
      # this one also becomes a part of the domain name
      EnvironmentName: !Join ['', [!Ref MyApp, '-env']]
      ApplicationName: !Ref MyApp
      TemplateName: !Ref ConfigurationTemplate
      VersionLabel: !Ref ApplicationVersion
  DNS:
    Type: AWS::Route53::RecordSetGroup
    DependsOn: MyAppEnvironment
    Properties:
      HostedZoneName: your.hosted.zone
      RecordSets:
      - Name: !Join ['.', [!Ref appName, !Ref domain]]
        Type: CNAME
        TTL: 900
        ResourceRecords: [!GetAtt [MyAppEnvironment, EndpointURL]]

Other elastic beanstalk snippets can be found here.

user_21980710

Because the instances are being created with an ASG they're unavailable as CloudFormation resources.

To overcome this you could:

  • create a script to retrieve all the public IP addresses of the instances associated with the ASG and setup Route53 CNAMEs in your hosted
  • alternatively if you want to keep using Custom::ResourceDNS, you could again retrieve the instance IP addresses and then pass them in to your CloudFormation stack as another parameter.
user_632950

Not sure how many brokers you need to spin up (I am not kafka-knowledgeable), but if it is a small set of brokers.....you can block a set of ENIs and attach them using the user-data script based on a pool of available ENIs. You can define a CNAME for the ENIs. Only limitation or risk is that you cannot enable the 'Delete on Termination' flag...else your ENI gets deleted too.

user_59586670
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