CODEWITHSUNDEEP
amazon-web-services
jagatjyoti
jagatjyoti

Reputation: 717

Retain the same set of Elastic IP and ENI in AWS

I'm working on a project where the nodes are heavily dependent on static networking as it's kind of a static cluster. Here it goes, there are 3 nodes in the cluster and are in auto-scaling but max count is 3 as the application running on top of them doesn't have the ability to scale automatically. Have created three Elastic IPs and keeping a track/maintaining it programatically. Likewise, for the ENIs wanted to have some mapping created to EIP (manual is also fine) only once. So that once any new node comes up, it attaches to it's EIP by the program I wrote and as EIP is mapped to ENI, it will automatically attach to it.

I understand that Elastic IP is just a floating public IP which remains constant and ENI is a network interface for the EC2.

Just curious if there is something out there which can make this work, which will reduce my pain of updating R53 everytime a new node joins the cluster.

Thanks in advance.

Upvotes: 0

Views: 243

Answers (2)

Adiii
Adiii

Reputation: 60074

If your cluster is depended on IP, then you can do the manual steps using cloud-init.

execute-user-data-ec2

Pass the Elastic IP as an input which needs to be associated with current isntance, associate the IP with a new instance and update route53 record.

Here is an example script that can help

#!/bin/bash

# find assoication using IP
function getAssociationIdByAddress() {
  if [ !  -z  $1  ]; then
    local association_id=$(aws --output text --query "Addresses[0].AssociationId" ec2 describe-addresses --public-ip $1)
    echo $association_id
  else
    echo "-1"
  fi
}

# deassociate from old instance
function disassociateAddressByAssociationId() {
  echo "Disassociating $1"
  aws ec2 disassociate-address --association-id $1
}

# assoicate address with new instance
function associateAddress() {
  my_instance_id=$(curl http://169.254.169.254/latest/meta-data/instance-id)
  aws ec2 associate-address --instance-id $my_instance_id --public-ip $1
}

Assigning Public IP, disassociating from current instance, if already allocated

  echo "Assigning Public IP"
  public_ip=55.X.X.X
  echo "Getting Association Id $public_ip"
  association_id=$(getAssociationIdByAddress $public_ip)

  if [ "None" = $association_id ] || [ "-1" = $association_id ] ; then
    echo "Not Associated"
  else
    echo "Association Id:" $association_id
    disassociateAddressByAssociationId $association_id
  fi
  associateAddress $public_ip

For adding or updating record from user data you can check aws-cli add or update DNS record

Upvotes: 1

Juned Ahsan
Juned Ahsan

Reputation: 68715

Relying on IP is not the best design as you are already facing the challenges associated to it. You should switch to hostnames, which are static in nature. You can configure and publish hostnames, which can remain the same but the mapped IP behind the scenes can change.

Yes you can utilize Route 53 in AWS to add A records for domain name to IP address mapping.

Upvotes: 0

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