How to have the CDK create only one Elastic IP address for use with a single EC2 instance (AWS CDK)

Question

I'm trying to create a Stack using the AWS CDK that will deploy a single EC2 instance, create an Elastic IP and then associate it with that instance. (MVP)

For reasons I don't understand, an elastic IP is created for each public subnet of the VPC my EC2 instance is within. I expect that only one should be created, not three.

Below is my simplified code:

const vpc = new Vpc(this, 'VPC');
const securityGroup = new SecurityGroup(this, 'SecurityGroup', {
  vpc,
});
const ec2Instance = new Instance(this, 'EC2Instance', {
  vpc,
  instanceType: new InstanceType('t2.small'),
  machineImage: ubuntuImage, // searched for elsewhere
  keyName: 'keynamehere',
  vpcSubnets: { subnets: [vpc.publicSubnets[0]] },
});
const eip = new CfnEIP(this, 'Server IP', {
  instanceId: ec2Instance.instanceId,
});

I've tried to use a CfnEIPAssociation instance of the 'instanceID' property within the CfnEIP but still have the same problem.

Any suggestions?

Answer 1

For me, I have to create the ec2 using the CfnInstance then use the ec2Instance.ref inside the CfnEIPAssociation .

    const instance = new ec2.CfnInstance(this, 'CccgEc2', {
      imageId: 'ami-07d0cf3af28718ef8',
      instanceType: 't2.micro',
      keyName: 'id_rsa',
      monitoring: false,
      securityGroupIds: [
        mySecurityGroup.securityGroupId
      ],
      subnetId: vpc.publicSubnets[0].subnetId,
      // iamInstanceProfile: 'ec2-role'
    });

    const eip = new ec2.CfnEIP(this, 'Server IP', {});

    new ec2.CfnEIPAssociation(this, 'ea', {
      eip: eip.ref,
      instanceId: instance.ref
    });

Answer 2

(Apologies, this is months after solving it)

I believe the issue was the vpcSubnets field, below is the working code I have today

const ec2Instance = new Instance(this, "Instance", {
      vpc: supportStack.vpc,
      instanceType: new InstanceType("t2.nano"),
      machineImage: ubuntuImage,
      securityGroup: supportStack.securityGroup,
      vpcSubnets: { subnetType: SubnetType.PUBLIC }, // 
      userData,
    });
    supportStack.bucket.grantRead(ec2Instance);
    new CfnEIPAssociation(this, "ElasticIpAssociation", {
      eip: eip.ref,
      instanceId: ec2Instance.instanceId,
    });