How to Use Elastic IP in AWS: Simple Guide

To use an Elastic IP in AWS, first allocate an Elastic IP address in your AWS account, then associate it with an EC2 instance or a network interface. This gives your resource a fixed public IP that stays the same even if you stop or restart the instance.

Syntax

Using Elastic IPs involves three main steps:

• Allocate Elastic IP: Reserve a public IP address in your AWS account.
• Associate Elastic IP: Attach the allocated IP to an EC2 instance or network interface.
• Disassociate and Release: Remove the IP from the resource and free it when no longer needed.

These steps can be done via AWS Console, CLI, or SDKs.

bash

aws ec2 allocate-address --domain vpc
aws ec2 associate-address --instance-id i-1234567890abcdef0 --allocation-id eipalloc-12345678
aws ec2 disassociate-address --association-id eipassoc-12345678
aws ec2 release-address --allocation-id eipalloc-12345678

Example

This example shows how to allocate an Elastic IP and associate it with an EC2 instance using AWS CLI.

bash

aws ec2 allocate-address --domain vpc
# Output includes AllocationId, e.g. eipalloc-12345678

aws ec2 associate-address --instance-id i-0abcdef1234567890 --allocation-id eipalloc-12345678
# Output includes AssociationId, e.g. eipassoc-87654321

Output

{
    "PublicIp": "203.0.113.25",
    "AllocationId": "eipalloc-12345678",
    "Domain": "vpc"
}
{
    "AssociationId": "eipassoc-87654321"
}

Common Pitfalls

• Not specifying --domain vpc when allocating Elastic IPs for VPC causes allocation in EC2-Classic, which is deprecated.
• Trying to associate an Elastic IP to an instance in a different region than the IP causes errors.
• Forgetting to release Elastic IPs when not in use leads to unnecessary charges.
• Associating Elastic IPs to stopped instances still incurs charges; disassociate if not needed.

bash

aws ec2 allocate-address
# Wrong: allocates in EC2-Classic (legacy)

aws ec2 allocate-address --domain vpc
# Correct: allocates in VPC

aws ec2 associate-address --instance-id i-0abcdef1234567890 --allocation-id eipalloc-12345678
# Make sure instance and allocation are in the same region

Quick Reference

Action	AWS CLI Command	Notes
Allocate Elastic IP	aws ec2 allocate-address --domain vpc	Reserves a public IP in your VPC
Associate Elastic IP	aws ec2 associate-address --instance-id --allocation-id	Attaches IP to EC2 instance
Disassociate Elastic IP	aws ec2 disassociate-address --association-id	Removes IP from instance
Release Elastic IP	aws ec2 release-address --allocation-id	Frees the IP to avoid charges

Key Takeaways

Always allocate Elastic IPs with --domain vpc for modern AWS setups.

Associate Elastic IPs only with instances in the same AWS region.

Release Elastic IPs when not in use to avoid extra costs.

Elastic IPs provide a fixed public IP that persists across instance stops and starts.

Use AWS CLI or Console to manage Elastic IPs easily.