Use DisassociateAddress with an AWS SDK or CLI

    /// <summary>
    /// Disassociate an Elastic IP address from an EC2 instance.
    /// </summary>
    /// <param name="associationId">The association Id.</param>
    /// <returns>A Boolean value indicating the success of the action.</returns>
    public async Task<bool> DisassociateIp(string associationId)
    {
        var response = await _amazonEC2.DisassociateAddressAsync(
            new DisassociateAddressRequest { AssociationId = associationId });
        return response.HttpStatusCode == HttpStatusCode.OK;
    }

###############################################################################
# function ec2_disassociate_address
#
# This function disassociates an Elastic IP address from an Amazon Elastic Compute Cloud (Amazon EC2) instance.
#
# Parameters:
#       -a association_id - The association ID that represents the association of the Elastic IP address with an instance.
#
# And:
#       0 - If successful.
#       1 - If it fails.
#
###############################################################################
function ec2_disassociate_address() {
  local association_id response

  # Function to display usage information
  function usage() {
    echo "function ec2_disassociate_address"
    echo "Disassociates an Elastic IP address from an Amazon Elastic Compute Cloud (Amazon EC2) instance."
    echo "  -a association_id - The association ID that represents the association of the Elastic IP address with an instance."
    echo ""
  }

  # Parse the command-line arguments
  while getopts "a:h" option; do
    case "${option}" in
      a) association_id="${OPTARG}" ;;
      h)
        usage
        return 0
        ;;
      \?)
        echo "Invalid parameter"
        usage
        return 1
        ;;
    esac
  done
  export OPTIND=1

  # Validate the input parameters
  if [[ -z "$association_id" ]]; then
    errecho "ERROR: You must provide an association ID with the -a parameter."
    return 1
  fi

  response=$(aws ec2 disassociate-address \
    --association-id "$association_id") || {
    aws_cli_error_log ${?}
    errecho "ERROR: AWS reports disassociate-address operation failed."
    errecho "$response"
    return 1
  }

  return 0
}

The utility functions used in this example.

###############################################################################
# function errecho
#
# This function outputs everything sent to it to STDERR (standard error output).
###############################################################################
function errecho() {
  printf "%s\n" "$*" 1>&2
}

##############################################################################
# function aws_cli_error_log()
#
# This function is used to log the error messages from the AWS CLI.
#
# The function expects the following argument:
#         $1 - The error code returned by the AWS CLI.
#
#  Returns:
#          0: - Success.
#
##############################################################################
function aws_cli_error_log() {
  local err_code=$1
  errecho "Error code : $err_code"
  if [ "$err_code" == 1 ]; then
    errecho "  One or more S3 transfers failed."
  elif [ "$err_code" == 2 ]; then
    errecho "  Command line failed to parse."
  elif [ "$err_code" == 130 ]; then
    errecho "  Process received SIGINT."
  elif [ "$err_code" == 252 ]; then
    errecho "  Command syntax invalid."
  elif [ "$err_code" == 253 ]; then
    errecho "  The system environment or configuration was invalid."
  elif [ "$err_code" == 254 ]; then
    errecho "  The service returned an error."
  elif [ "$err_code" == 255 ]; then
    errecho "  255 is a catch-all error."
  fi

  return 0
}

To disassociate an Elastic IP addresses in EC2-Classic

This example disassociates an Elastic IP address from an instance in EC2-Classic. If the command succeeds, no output is returned.

Command:

aws ec2 disassociate-address --public-ip 198.51.100.0

To disassociate an Elastic IP address in EC2-VPC

This example disassociates an Elastic IP address from an instance in a VPC. If the command succeeds, no output is returned.

Command:

aws ec2 disassociate-address --association-id eipassoc-2bebb745

    /**
     * Disassociates an Elastic IP address from an instance asynchronously.
     *
     * @param associationId The ID of the association you want to disassociate.
     * @return a {@link CompletableFuture} representing the asynchronous operation of disassociating the address. The
     *         {@link CompletableFuture} will complete with a {@link DisassociateAddressResponse} when the operation is
     *         finished.
     * @throws RuntimeException if the disassociation of the address fails.
     */
    public CompletableFuture<DisassociateAddressResponse> disassociateAddressAsync(String associationId) {
        Ec2AsyncClient ec2 = getAsyncClient();
        DisassociateAddressRequest addressRequest = DisassociateAddressRequest.builder()
            .associationId(associationId)
            .build();

        // Disassociate the address asynchronously.
        CompletableFuture<DisassociateAddressResponse> response = ec2.disassociateAddress(addressRequest);
        response.whenComplete((resp, ex) -> {
            if (ex != null) {
               throw new RuntimeException("Failed to disassociate address", ex);
            }
        });

        return response;
    }

import { DisassociateAddressCommand, EC2Client } from "@aws-sdk/client-ec2";

/**
 * Disassociate an Elastic IP address from an instance.
 * @param {{ associationId: string }} options
 */
export const main = async ({ associationId }) => {
  const client = new EC2Client({});
  const command = new DisassociateAddressCommand({
    // You can also use PublicIp, but that is for EC2 classic which is being retired.
    AssociationId: associationId,
  });

  try {
    await client.send(command);
    console.log("Successfully disassociated address");
  } catch (caught) {
    if (
      caught instanceof Error &&
      caught.name === "InvalidAssociationID.NotFound"
    ) {
      console.warn(`${caught.message}.`);
    } else {
      throw caught;
    }
  }
};

suspend fun disassociateAddressSc(associationIdVal: String?) {
    val addressRequest =
        DisassociateAddressRequest {
            associationId = associationIdVal
        }
    Ec2Client { region = "us-west-2" }.use { ec2 ->
        ec2.disassociateAddress(addressRequest)
        println("You successfully disassociated the address!")
    }
}

Example 1: This example disassociates the specified Elastic IP address from the specified instance in a VPC.

Unregister-EC2Address -AssociationId eipassoc-12345678

Example 2: This example disassociates the specified Elastic IP address from the specified instance in EC2-Classic.

Unregister-EC2Address -PublicIp 203.0.113.17

class ElasticIpWrapper:
    """Encapsulates Amazon Elastic Compute Cloud (Amazon EC2) Elastic IP address actions using the client interface."""

    class ElasticIp:
        """Represents an Elastic IP and its associated instance."""

        def __init__(
            self, allocation_id: str, public_ip: str, instance_id: Optional[str] = None
        ) -> None:
            """
            Initializes the ElasticIp object.

            :param allocation_id: The allocation ID of the Elastic IP.
            :param public_ip: The public IP address of the Elastic IP.
            :param instance_id: The ID of the associated EC2 instance, if any.
            """
            self.allocation_id = allocation_id
            self.public_ip = public_ip
            self.instance_id = instance_id

    def __init__(self, ec2_client: Any) -> None:
        """
        Initializes the ElasticIpWrapper with an EC2 client.

        :param ec2_client: A Boto3 Amazon EC2 client. This client provides low-level
                           access to AWS EC2 services.
        """
        self.ec2_client = ec2_client
        self.elastic_ips: List[ElasticIpWrapper.ElasticIp] = []

    @classmethod
    def from_client(cls) -> "ElasticIpWrapper":
        """
        Creates an ElasticIpWrapper instance with a default EC2 client.

        :return: An instance of ElasticIpWrapper initialized with the default EC2 client.
        """
        ec2_client = boto3.client("ec2")
        return cls(ec2_client)


    def disassociate(self, allocation_id: str) -> None:
        """
        Removes an association between an Elastic IP address and an instance. When the
        association is removed, the instance is assigned a new public IP address.

        :param allocation_id: The allocation ID of the Elastic IP to disassociate.
        :raises ClientError: If the disassociation fails, such as when the association ID is not found.
        """
        elastic_ip = self.get_elastic_ip_by_allocation(self.elastic_ips, allocation_id)
        if elastic_ip is None or elastic_ip.instance_id is None:
            logger.info(
                f"No association found for Elastic IP with allocation ID {allocation_id}."
            )
            return

        try:
            # Retrieve the association ID before disassociating
            response = self.ec2_client.describe_addresses(AllocationIds=[allocation_id])
            association_id = response["Addresses"][0].get("AssociationId")

            if association_id:
                self.ec2_client.disassociate_address(AssociationId=association_id)
                elastic_ip.instance_id = None  # Remove the instance association
            else:
                logger.info(
                    f"No Association ID found for Elastic IP with allocation ID {allocation_id}."
                )

        except ClientError as err:
            if err.response["Error"]["Code"] == "InvalidAssociationID.NotFound":
                logger.error(
                    f"Failed to disassociate Elastic IP {allocation_id} "
                    "because the specified association ID for the Elastic IP address was not found. "
                    "Verify the association ID and ensure the Elastic IP is currently associated with a "
                    "resource before attempting to disassociate it."
                )
            raise

    pub async fn disassociate_ip_address(&self, association_id: &str) -> Result<(), EC2Error> {
        self.client
            .disassociate_address()
            .association_id(association_id)
            .send()
            .await?;
        Ok(())
    }