How to assign EIP to Autoscaling Group of VPC in Cloudformation template

Question

I want to assign one of my reserved Elastic IP's(ec2 classic ip) to Autoscaling group in VPC. Using AWS Cli I moved ip to vpc:

$ aws ec2 move-address-to-vpc --public-ip 23.23.23.23

And saw in aws concole, that this IP passed to VPC. And Assigned in tags of AutoscalingGroup in Cloudformation template in Resources:

"Process": {
        "Type" : "AWS::AutoScaling::AutoScalingGroup",
        "Properties": {
            "LaunchConfigurationName": {"Ref": "PreprocessorLC"},
            "LoadBalancerNames": [{"Ref": "ProcessELB"}],
            "VPCZoneIdentifier" : [{ "Fn::Join" : [",", [ { "Ref" : "PublicSubnet1"}, { "Ref" : "PublicSubnet2"} ]]}],
            "AvailabilityZones": {"Ref": "AZs"},
            "MinSize" : "1",
            "MaxSize" : "1",
            "HealthCheckGracePeriod": 300,
            "Tags" : [
                {"Key": "Name", "Value": {"Fn::Join": ["", [{"Ref": "Env"}, "-Process"]]}, "PropagateAtLaunch": true},
                {"Key": "WorkersScalingGroup", "Value": {"Fn::Join": ["", ["Offering-", {"Ref": "Env"},  "-Process-Worker"]]}, "PropagateAtLaunch": true},
                {"Key": "EIP", "Value": {"Ref": "ProcessIP"}, "PropagateAtLaunch": true},
                {"Key": "Environment", "Value": {"Ref": "Env"}, "PropagateAtLaunch": true}
            ]
        }
    }

And added value of "ProcessIP" in Parameters:

"ProcessIP":{
            "Description": "DEV: 23.23.23.23",
            "Type": "String",
            "Default": "23.23.23.23",
            "AllowedValues": ["23.23.23.23"]
}

And it doesn't worked. Still get random IP. If someone can tell where I'm wrong or what should to add for make it work?

Thanks!

Answer 1

In my case, I needed to keep a bank of unassigned EIPs and randomly assign them to the EC2 when they boot. That way I always know my servers will be using a specific list of IPs that I can whitelist in other places.

If you create several EIPs named "prod-pool" you can then use this script.

apt install -y jq awscli
ALLOCATION_ID=`aws ec2 describe-addresses --filters="Name=tag:Name,Values=prod-pool" | jq -r '.Addresses[] | "\(.InstanceId) \(.AllocationId)"' | grep null | awk '{print $2}' | xargs shuf -n1 -e`

if [ ! -z $ALLOCATION_ID ]; then
    aws ec2 associate-address --instance-id $INSTANCE_ID --allocation-id $ALLOCATION_ID --allow-reassociation
fi

You can attached this policy to your IAM user

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "AllowEIPAttachment",
      "Effect": "Allow",
      "Resource": [
        "*"
      ],
      "Action": [
        "ec2:AssociateAddress",
        "ec2:DisassociateAddress"
      ]
    }
  ]
}

Answer 2

Here is simple bash script:

#!/bin/sh
# Region in Which instance is running
EC2_REGION='us-east-1'
AWS_ACCESS_KEY='xxxxxxxxxxxx'
AWS_SECRET_ACCESS_KEY='xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'

#Instance ID captured through Instance meta data
InstanceID=`/usr/bin/curl -s http://169.254.169.254/latest/meta-data/instance-id`

#Elastic IP captured through the EIP instance tag
Elastic_IP=`/opt/aws/apitools/ec2/bin/ec2-describe-tags -O $AWS_ACCESS_KEY -W $AWS_SECRET_ACCESS_KEY --filter resource-id=$InstanceID --filter key='EIP' | cut -f5`
Allocate_ID=`/opt/aws/apitools/ec2/bin/ec2-describe-tags -O $AWS_ACCESS_KEY -W $AWS_SECRET_ACCESS_KEY --filter resource-id=$InstanceID --filter key="AllocationID" | cut -f5`

#Assigning Elastic IP to Instance
aws ec2 associate-address --instance-id $InstanceID --allocation-id $Allocate_ID

Answer 3

You need to explicitly associate the Elastic IP address with your desired EC2 instance. You can do this in a userdata script at launch time, or externally through other scripting or Configuration Management.

PropagateAtLaunch simply propagates tags from the Auto Scaling Group to any instances that are launched as a result of Auto Scaling actions. I'm not aware of any magic that would cause a tagged Elastic IP address to be associated with a launched instance.

See more discussion and examples of launch time scripting with EIPs here.

Answer 4

I created a AWS Lambda function which will automatically bind an Elastic IP address from a pool to instance of an autoscaling group. This alleviates the need to grab an EIP address in the bootscript of the instances. For a complete description check out https://binx.io/blog/2019/09/02/how-to-dynamically-bind-elastic-ip-addresses-to-an-auto-scaling-group/