What is an Elastic IP?

An Elastic IP (EIP) is a static, public IPv4 address designed specifically for dynamic cloud computing. Unlike regular public IP addresses, which can change when an instance stops and starts, an Elastic IP remains static. Key characteristics include:

• Account Association: EIPs are associated with your AWS account rather than being tied to a specific instance by default.
• Remapping Capability: You can remap an EIP from one instance to another within the same AWS region.
• Persistence: The EIP remains allocated to your account until explicitly released.

Elastic IPs provide flexibility and reliability for applications that require a fixed public IP address, making them ideal for certain high-availability and disaster recovery scenarios.

Use Cases

1. High Availability

Elastic IPs are crucial for applications that demand high availability. They allow you to quickly remap the IP address to a backup instance if the primary one fails.

Example:

• Your primary EC2 instance fails.
• Remap the EIP to a backup EC2 instance in the same region.
• Traffic seamlessly resumes without requiring DNS changes.

2. Static IP for Critical Services

EIPs are ideal for hosting services that require a fixed IP, such as:

• Setting up DNS records.
• Scenarios requiring IP whitelisting for access control.
• Integration with external services that rely on a constant IP address.

3. Disaster Recovery

Elastic IPs are an integral part of failover strategies. They provide a DNS-independent recovery option, ensuring minimal downtime.

Example:

• In a disaster recovery setup, traffic can be redirected to a secondary environment by remapping the EIP.

Best Practices

1. Cost Management

Elastic IPs are cost-effective when used appropriately, but AWS charges apply under specific circumstances:

• Free:
  • When associated with a running instance.
  • If only one EIP is allocated per instance.
• Charged:
  • When the EIP is not associated with any instance.
  • If associated with a stopped instance.
  • When multiple EIPs are allocated to the same instance.

2. Resource Management

Efficient resource management ensures you make the most of EIPs:

Do:

• Use DNS names instead of EIPs when possible.
• Release unused EIPs to avoid unnecessary charges.
• Tag EIPs for better tracking and management.
• Use EIPs only when absolutely necessary.

Don’t:

• Allocate EIPs for temporary use cases.
• Keep unassociated EIPs idle.
• Use EIPs for internal communication; private IPs are better suited for this.

3. High Availability Setup

Follow this recommended pattern to ensure high availability:

1. Create a primary EC2 instance.
2. Create a backup EC2 instance.
3. Allocate an Elastic IP.
4. Associate the EIP with the primary instance.
5. Set up health monitoring.
6. Use a script or automation to move the EIP to the backup instance if the primary fails.

4. Security Considerations

Secure your Elastic IPs to prevent misuse:

• Use security groups to control access to resources associated with EIPs.
• Monitor EIP usage and access patterns.
• Document which services and applications use each EIP.
• Implement strict IAM policies for EIP allocation and management.

Limits and Quotas

Be aware of the following constraints when using Elastic IPs:

• Default Limit: 5 Elastic IPs per region (can request an increase).
• Region-Specific: EIPs cannot be moved between regions.
• Mapping Constraints: Each EIP maps to one primary private IP per instance.
• Connectivity Interruption: Remapping an EIP between instances may cause brief connectivity disruptions.

Consider Modern Alternatives

While Elastic IPs are useful, they might not always align with modern cloud architecture. For scalable and resilient systems, consider using:

DNS

• Route 53 provides advanced routing options (geolocation, failover, weighted routing) and integrates seamlessly with Auto Scaling.

Elastic Load Balancers (ELBs)

• Distribute traffic across multiple targets, support auto-scaling, and provide built-in health checks.

These alternatives reduce dependency on static IPs, improve scalability, and align with modern architectural practices.

Conclusion

Elastic IPs remain a powerful tool in AWS for applications requiring a fixed IP address, high availability, or disaster recovery capabilities. However, they should be used judiciously to manage costs and resources effectively. For most modern use cases, leveraging DNS and Elastic Load Balancers offers greater flexibility, scalability, and alignment with cloud-native best practices.