Elastic IP Address Specialized2008年〜
A static public IPv4 address that you associate with EC2 instances
What It Does
Elastic IP Address is a static public IPv4 address allocated to your AWS account. Since the address doesn't change when you stop and start EC2 instances, you don't need to update DNS records or firewall allow lists. You can also reassign the address between instances.
Use Cases
It is used for running web servers that require a fixed IP address, registering IP addresses in whitelists for external system integrations, and failover configurations where the IP is reassigned to a standby instance during failures.
Everyday Analogy
Think of it like mobile number portability. Even when you change phones (swap instances), your phone number (IP address) stays the same. Since you can transfer the number to a different device, there's no need to notify everyone of a new number.
What Is Elastic IP?
Elastic IP Address (EIP) is a static public IPv4 address tied to your AWS account. Normally, an EC2 instance's public IP address changes when you stop and start it, but associating an EIP keeps the address fixed. This eliminates the need to change DNS A records and enables stable external access.
Pricing and Considerations
Since February 2024, all public IPv4 addresses are charged at $0.005 per hour. Charges apply even when an EIP is allocated but not associated with an EC2 instance, so it is important to release unused EIPs promptly. The default limit is 5 per region per account, but this can be increased by request. For detailed implementation guidance on pricing and considerations, specialized books on Amazon provide thorough coverage.
Getting Started
Click 'Allocate Elastic IP address' in the 'Elastic IP addresses' section of the EC2 console. Select the allocated EIP and click 'Associate Elastic IP address' to assign it to an EC2 instance. For failover, you can reassign it to a different instance by disassociating and re-associating.
Things to Watch Out For
- Since February 2024, all public IPv4 addresses incur hourly charges whether in use or not
- Allocated but unassociated EIPs waste money, so release unused EIPs promptly
- If a fixed IP is not needed, consider DNS-based routing with ELB or CloudFront instead
