Use AssociateAddress with an AWS SDK or CLI

    /// <summary>
    /// Associates an Elastic IP address with an instance. When this association is
    /// created, the Elastic IP's public IP address is immediately used as the public
    /// IP address of the associated instance.
    /// </summary>
    /// <param name="allocationId">The allocation Id of an Elastic IP address.</param>
    /// <param name="instanceId">The instance Id of the EC2 instance to
    /// associate the address with.</param>
    /// <returns>The association Id that represents
    /// the association of the Elastic IP address with an instance.</returns>
    public async Task<string> AssociateAddress(string allocationId, string instanceId)
    {
        try
        {
            var request = new AssociateAddressRequest
            {
                AllocationId = allocationId,
                InstanceId = instanceId
            };

            var response = await _amazonEC2.AssociateAddressAsync(request);
            return response.AssociationId;
        }
        catch (AmazonEC2Exception ec2Exception)
        {
            if (ec2Exception.ErrorCode == "InvalidInstanceId")
            {
                _logger.LogError(
                    $"InstanceId is invalid, unable to associate address. {ec2Exception.Message}");
            }

            throw;
        }
        catch (Exception ex)
        {
            _logger.LogError(
                $"An error occurred while associating the Elastic IP.: {ex.Message}");
            throw;
        }
    }

###############################################################################
# function ec2_associate_address
#
# This function associates an Elastic IP address with an Amazon Elastic Compute Cloud (Amazon EC2) instance.
#
# Parameters:
#       -a allocation_id - The allocation ID of the Elastic IP address to associate.
#       -i instance_id - The ID of the EC2 instance to associate the Elastic IP address with.
#
# Returns:
#       0 - If successful.
#       1 - If it fails.
#
###############################################################################
function ec2_associate_address() {
  local allocation_id instance_id response

  # Function to display usage information
  function usage() {
    echo "function ec2_associate_address"
    echo "Associates an Elastic IP address with an Amazon Elastic Compute Cloud (Amazon EC2) instance."
    echo "  -a allocation_id - The allocation ID of the Elastic IP address to associate."
    echo "  -i instance_id - The ID of the EC2 instance to associate the Elastic IP address with."
    echo ""
  }

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

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

  if [[ -z "$instance_id" ]]; then
    errecho "ERROR: You must provide an instance ID with the -i parameter."
    return 1
  fi

  # Associate the Elastic IP address
  response=$(aws ec2 associate-address \
    --allocation-id "$allocation_id" \
    --instance-id "$instance_id" \
    --query "AssociationId" \
    --output text) || {
    aws_cli_error_log ${?}
    errecho "ERROR: AWS reports associate-address operation failed."
    errecho "$response"
    return 1
  }

  echo "$response"
  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
}

    Aws::EC2::EC2Client ec2Client(clientConfiguration);

//! Associate an Elastic IP address with an EC2 instance.
/*!
  \param instanceId: An EC2 instance ID.
  \param allocationId: An Elastic IP allocation ID.
  \param[out] associationID: String to receive the association ID.
  \param clientConfiguration: AWS client configuration.
  \return bool: True if the address was associated with the instance; otherwise, false.
 */
bool AwsDoc::EC2::associateAddress(const Aws::String &instanceId, const Aws::String &allocationId,
                                   Aws::String &associationID,
                                   const Aws::Client::ClientConfiguration &clientConfiguration) {
    Aws::EC2::EC2Client ec2Client(clientConfiguration);

    Aws::EC2::Model::AssociateAddressRequest request;
    request.SetInstanceId(instanceId);
    request.SetAllocationId(allocationId);

    Aws::EC2::Model::AssociateAddressOutcome outcome = ec2Client.AssociateAddress(request);

    if (!outcome.IsSuccess()) {
        std::cerr << "Failed to associate address " << allocationId <<
                  " with instance " << instanceId << ": " <<
                  outcome.GetError().GetMessage() << std::endl;
    } else {
        std::cout << "Successfully associated address " << allocationId <<
                  " with instance " << instanceId << std::endl;
        associationID = outcome.GetResult().GetAssociationId();
    }

    return outcome.IsSuccess();
}

To associate an Elastic IP addresses in EC2-Classic

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

Command:

aws ec2 associate-address --instance-id i-07ffe74c7330ebf53 --public-ip 198.51.100.0

To associate an Elastic IP address in EC2-VPC

This example associates an Elastic IP address with an instance in a VPC.

Command:

aws ec2 associate-address --instance-id i-0b263919b6498b123 --allocation-id eipalloc-64d5890a

Output:

{
    "AssociationId": "eipassoc-2bebb745"
}

This example associates an Elastic IP address with a network interface.

Command:

aws ec2 associate-address --allocation-id eipalloc-64d5890a --network-interface-id eni-1a2b3c4d

This example associates an Elastic IP with a private IP address that's associated with a network interface.

Command:

aws ec2 associate-address --allocation-id eipalloc-64d5890a --network-interface-id eni-1a2b3c4d --private-ip-address 10.0.0.85

    /**
     * Associates an Elastic IP address with an EC2 instance asynchronously.
     *
     * @param instanceId    the ID of the EC2 instance to associate the Elastic IP address with
     * @param allocationId  the allocation ID of the Elastic IP address to associate
     * @return a {@link CompletableFuture} that completes with the association ID when the operation is successful,
     *         or throws a {@link RuntimeException} if the operation fails
     */
    public CompletableFuture<String> associateAddressAsync(String instanceId, String allocationId) {
        AssociateAddressRequest associateRequest = AssociateAddressRequest.builder()
            .instanceId(instanceId)
            .allocationId(allocationId)
            .build();

        CompletableFuture<AssociateAddressResponse> responseFuture = getAsyncClient().associateAddress(associateRequest);
        return responseFuture.thenApply(response -> {
            if (response.associationId() != null) {
                return response.associationId();
            } else {
                throw new RuntimeException("Association ID is null after associating address.");
            }
        }).whenComplete((result, ex) -> {
            if (ex != null) {
                throw new RuntimeException("Failed to associate address", ex);
            }
        });
    }

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

/**
 * Associates an Elastic IP address, or carrier IP address (for instances that are in subnets in Wavelength Zones)
 * with an instance or a network interface.
 * @param {{ instanceId: string, allocationId: string }} options
 */
export const main = async ({ instanceId, allocationId }) => {
  const client = new EC2Client({});
  const command = new AssociateAddressCommand({
    // You need to allocate an Elastic IP address before associating it with an instance.
    // You can do that with the AllocateAddressCommand.
    AllocationId: allocationId,
    // You need to create an EC2 instance before an IP address can be associated with it.
    // You can do that with the RunInstancesCommand.
    InstanceId: instanceId,
  });

  try {
    const { AssociationId } = await client.send(command);
    console.log(
      `Address with allocation ID ${allocationId} is now associated with instance ${instanceId}.`,
      `The association ID is ${AssociationId}.`,
    );
  } catch (caught) {
    if (
      caught instanceof Error &&
      caught.name === "InvalidAllocationID.NotFound"
    ) {
      console.warn(
        `${caught.message}. Did you provide the ID of a valid Elastic IP address AllocationId?`,
      );
    } else {
      throw caught;
    }
  }
};

suspend fun associateAddressSc(
    instanceIdVal: String?,
    allocationIdVal: String?,
): String? {
    val associateRequest =
        AssociateAddressRequest {
            instanceId = instanceIdVal
            allocationId = allocationIdVal
        }

    Ec2Client { region = "us-west-2" }.use { ec2 ->
        val associateResponse = ec2.associateAddress(associateRequest)
        return associateResponse.associationId
    }
}

Example 1: This example associates the specified Elastic IP address with the specified instance in a VPC.

C:\> Register-EC2Address -InstanceId i-12345678 -AllocationId eipalloc-12345678

Output:

eipassoc-12345678

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

C:\> Register-EC2Address -InstanceId i-12345678 -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 associate(
        self, allocation_id: str, instance_id: str
    ) -> Union[Dict[str, Any], None]:
        """
        Associates an Elastic IP address with an instance. When this association is
        created, the Elastic IP's public IP address is immediately used as the public
        IP address of the associated instance.

        :param allocation_id: The allocation ID of the Elastic IP.
        :param instance_id: The ID of the Amazon EC2 instance.
        :return: A response that contains the ID of the association, or None if no Elastic IP is found.
        :raises ClientError: If the association fails, such as when the instance ID is not found.
        """
        elastic_ip = self.get_elastic_ip_by_allocation(self.elastic_ips, allocation_id)
        if elastic_ip is None:
            logger.info(f"No Elastic IP found with allocation ID {allocation_id}.")
            return None

        try:
            response = self.ec2_client.associate_address(
                AllocationId=allocation_id, InstanceId=instance_id
            )
            elastic_ip.instance_id = (
                instance_id  # Track the instance associated with this Elastic IP.
            )
        except ClientError as err:
            if err.response["Error"]["Code"] == "InvalidInstanceID.NotFound":
                logger.error(
                    f"Failed to associate Elastic IP {allocation_id} with {instance_id} "
                    "because the specified instance ID does not exist or has not propagated fully. "
                    "Verify the instance ID and try again, or wait a few moments before attempting to "
                    "associate the Elastic IP address."
                )
            raise
        return response

# Associates an Elastic IP address with an Amazon Elastic Compute Cloud
# (Amazon EC2) instance.
#
# Prerequisites:
#
# - The allocation ID corresponding to the Elastic IP address.
# - The Amazon EC2 instance.
#
# @param ec2_client [Aws::EC2::Client] An initialized EC2 client.
# @param allocation_id [String] The ID of the allocation corresponding to
#   the Elastic IP address.
# @param instance_id [String] The ID of the instance.
# @return [String] The assocation ID corresponding to the association of the
#   Elastic IP address to the instance.
# @example
#   puts allocate_elastic_ip_address(
#     Aws::EC2::Client.new(region: 'us-west-2'),
#     'eipalloc-04452e528a66279EX',
#     'i-033c48ef067af3dEX')
def associate_elastic_ip_address_with_instance(
  ec2_client,
  allocation_id,
  instance_id
)
  response = ec2_client.associate_address(
    allocation_id: allocation_id,
    instance_id: instance_id
  )
  response.association_id
rescue StandardError => e
  puts "Error associating Elastic IP address with instance: #{e.message}"
  'Error'
end

    pub async fn associate_ip_address(
        &self,
        allocation_id: &str,
        instance_id: &str,
    ) -> Result<AssociateAddressOutput, EC2Error> {
        let response = self
            .client
            .associate_address()
            .allocation_id(allocation_id)
            .instance_id(instance_id)
            .send()
            .await?;
        Ok(response)
    }

    TRY.
        oo_result = lo_ec2->associateaddress(                         " oo_result is returned for testing purposes. "
            iv_allocationid = iv_allocation_id
            iv_instanceid = iv_instance_id
        ).
        MESSAGE 'Associated an Elastic IP address with an EC2 instance.' TYPE 'I'.
      CATCH /aws1/cx_rt_service_generic INTO DATA(lo_exception).
        DATA(lv_error) = |"{ lo_exception->av_err_code }" - { lo_exception->av_err_msg }|.
        MESSAGE lv_error TYPE 'E'.
    ENDTRY.