An Elastic IP address is a static IPv4 address designed for dynamic cloud computing.

An Elastic IP address is associated with your AWS account. With an Elastic IP address, you can mask the failure of an instance or software by rapidly remapping the address to another instance in your account.

An Elastic IP address is a public IPv4 address, which is reachable from the internet. If your instance does not have a public IPv4 address, you can associate an Elastic IP address with your instance to enable communication with the internet. For example, this allows you to connect to your instance from your local computer.

Elastic IP Address Basics

The following are the basic characteristics of an Elastic IP address:

  • To use an Elastic IP address, you first allocate one to your account, and then associate it with your instance or a network interface.
  • When you associate an Elastic IP address with an instance, it is also associated with the instance’s primary network interface. When you associate an Elastic IP address with a network interface that is attached to an instance, it is also associated with the instance.
  • When you associate an Elastic IP address with an instance or its primary network interface, the instance’s public IPv4 address (if it had one) is released back into Amazon’s pool of public IPv4 addresses. You cannot reuse a public IPv4 address, and you cannot convert a public IPv4 address to an Elastic IP address. For more information, see Public IPv4 addresses and external DNS hostnames.
  • You can disassociate an Elastic IP address from a resource, and reassociate it with a different resource. Any open connections to an instance continue to work for a time even after you disassociate its Elastic IP address and reassociate it with another instance. We recommend that you reopen these connections using the reassociated Elastic IP address.
  • A disassociated Elastic IP address remains allocated to your account until you explicitly release it.
  • To ensure efficient use of Elastic IP addresses, we impose a small hourly charge if an Elastic IP address is not associated with a running instance, or if it is associated with a stopped instance or an unattached network interface. While your instance is running, you are not charged for one Elastic IP address associated with the instance, but you are charged for any additional Elastic IP addresses associated with the instance. For more information, see Amazon EC2 Pricing.
  • An Elastic IP address is for use in a specific network border group only.
  • When you associate an Elastic IP address with an instance that previously had a public IPv4 address, the public DNS host name of the instance changes to match the Elastic IP address.
  • We resolve a public DNS host name to the public IPv4 address or the Elastic IP address of the instance outside the network of the instance, and to the private IPv4 address of the instance from within the network of the instance.
  • When you allocate an Elastic IP address from an IP address pool that you have brought to your AWS account, it does not count toward your Elastic IP address limits.
  • When you allocate the Elastic IP addresses, you can associate the Elastic IP addresses with a network border group. This is the location from which we advertise the CIDR block. Setting the network border group limits the CIDR block to this group. If you do not specify the network border group, we set the border group containing all of the Availability Zones in the Region (for example, us-west-2).
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