AWS Elastic IP manager

The elastic-ip-manager, manages the assignment of a pool of Elastic IP addresses to instances. When the instance is stopped or terminated, the elastic ip address is removed. When a new instance is started, an elastic ip is assigned to it.

Who does it work?

The manager will listen to all EC2 instance state change notifications. When an instance with the tag elastic-ip-manager-pool reaches the state running, it will assign a free elastic ip addresses with the same tag and tag value.

How do I use it?

You can start using the elastic IP manager, in two simple steps:

1. create a pool of tagged elastic IP addresses
2. create an auto scaling group of tagged instances OR adjust autoscaling group of existing ones

deploy the elastic-ip-manager

To deploy the provider, type: ~

cd ..
git clone https://github.com/binxio/ec2-elastic-ip-manager.git
cd ec2-elastic-ip-manager
LAMBDA_BUCKET_PREFIX=binxio-public
LAMBDA_BUCKET_REGION=eu-central-1    
make S3_BUCKET_PREFIX=${LAMBDA_BUCKET_PREFIX:-binxio-public} AWS_REGION=${LAMBDA_BUCKET_REGION:-eu-central-1} deploy

aws cloudformation create-stack \
        --capabilities CAPABILITY_IAM \
        --stack-name elastic-ip-manager \
        --template-body file://./cloudformation/elastic-ip-manager.yaml \
        --parameters ParameterKey=LambdaS3Bucket,ParameterValue=${LAMBDA_BUCKET_PREFIX}-${LAMBDA_BUCKET_REGION} \
        --parameters ParameterKey=CFNCustomProviderZipFileName,ParameterValue=lambdas/elastic-ip-manager-latest.zip

Create a pool of Elastic IP addresses

Create a pool of elastic ip addresses, and tag them with an elastic-ip-manager-pool value:

  EIP1:
    Type: AWS::EC2::EIP
    Properties:
      Domain: vpc
      Tags:
        -
          Key: "elastic-ip-manager-pool"
          Value: bastion

Create an auto scaling group

Create an auto scaling group and apply the tag elastic-ip-manager-pool to all the instances:

  AutoScalingGroup:
    Type: AWS::AutoScaling::AutoScalingGroup
    Properties:
      ...
      Tags:
        - Key: elastic-ip-manager-pool
          Value: bastion
          PropagateAtLaunch: true

The manager will automatically associate elastic ip addresses to instance tagged with elastic-ip-manager-pool. It does this by subscribing to EC2 state change events. It will not do anything on instances without the tag elastic-ip-manager-pool. The elastic IP manager also syncs the state every 5 minutes, to ensure that we are eventually consistent in the face of errors.

Adjust existing auto scaling group

If an auto scaling group with instances already exist,

aws autoscaling create-or-update-tags --tags ResourceId=elastic-ip-manager-demo,ResourceType=auto-scaling-group,Key=elastic-ip-manager-pool,Value=bastion,PropagateAtLaunch=true 

instances=$(aws autoscaling describe-auto-scaling-groups --auto-scaling-group-names elastic-ip-manager-demo | jq -r '..|.InstanceId?| select(. != null)' | tr '\n' ' ')

aws ec2 create-tags --resources `echo $instances` --tags Key=elastic-ip-manager-pool,Value=bastion

That is all. If you want to see it all in action, deploy the demo.

Deploy the demo

Using CloudFormation Stack

Run these commands to deploy the demo using CloudFormation Stack:

export VPC_ID=$(aws ec2  --output text --query 'Vpcs[?IsDefault].VpcId' describe-vpcs)
export SUBNET_IDS=$(aws ec2 describe-subnets --output text \
  --filters Name=vpc-id,Values=$VPC_ID Name=default-for-az,Values=true --query 'Subnets[?MapPublicIpOnLaunch].SubnetId' \
  | tr '\t', '\,')

aws cloudformation create-stack --stack-name elastic-ip-manager-demo \
     --template-body file://./cloudformation/demo-stack.yaml \
     --parameters ParameterKey=VPC,ParameterValue=$VPC_ID ParameterKey=Subnets,ParameterValue=\"$SUBNET_IDS\"

Using terraform

Make sure you have terraform 0.12+ installed and run these commands:

export VPC_ID=$(aws ec2  --output text --query 'Vpcs[?IsDefault].VpcId' describe-vpcs)
export SUBNET_LIST=$(aws ec2 describe-subnets --output json \
  --filters Name=vpc-id,Values=$VPC_ID Name=default-for-az,Values=true --query 'Subnets[?MapPublicIpOnLaunch].SubnetId' \
  | tr -d '\n ')

cd ./terraform/demo
terraform init
terraform apply -var="vpc_id=$VPC_ID" -var="subnets=$SUBNET_LIST"

Alternatives

There are two alternative solutions to achieve the same functionality:

1. use a network load balancer
2. associate an address on instance startup In my use case, I did not want to spent money on keeping an NLB running nor give the instance all the permissions to associate an EIP to itself.