Use SetDesiredCapacity with an AWS SDK or CLI

    /// <summary>
    /// Set the desired capacity of an Auto Scaling group.
    /// </summary>
    /// <param name="groupName">The name of the Auto Scaling group.</param>
    /// <param name="desiredCapacity">The desired capacity for the Auto
    /// Scaling group.</param>
    /// <returns>A Boolean value indicating the success of the action.</returns>
    public async Task<bool> SetDesiredCapacityAsync(
        string groupName,
        int desiredCapacity)
    {
        var capacityRequest = new SetDesiredCapacityRequest
        {
            AutoScalingGroupName = groupName,
            DesiredCapacity = desiredCapacity,
        };

        var response = await _amazonAutoScaling.SetDesiredCapacityAsync(capacityRequest);
        Console.WriteLine($"You have set the DesiredCapacity to {desiredCapacity}.");

        return response.HttpStatusCode == System.Net.HttpStatusCode.OK;
    }

        Aws::Client::ClientConfiguration clientConfig;
        // Optional: Set to the AWS Region (overrides config file).
        // clientConfig.region = "us-east-1";

    Aws::AutoScaling::AutoScalingClient autoScalingClient(clientConfig);

        Aws::AutoScaling::Model::SetDesiredCapacityRequest request;
        request.SetAutoScalingGroupName(groupName);
        request.SetDesiredCapacity(2);

        Aws::AutoScaling::Model::SetDesiredCapacityOutcome outcome =
                autoScalingClient.SetDesiredCapacity(request);

        if (!outcome.IsSuccess()) {
            std::cerr << "Error with AutoScaling::SetDesiredCapacityRequest. "
                      << outcome.GetError().GetMessage()
                      << std::endl;

        }

To set the desired capacity for an Auto Scaling group

This example sets the desired capacity for the specified Auto Scaling group.

aws autoscaling set-desired-capacity \
    --auto-scaling-group-name my-asg \
    --desired-capacity 2 \
    --honor-cooldown

This command returns to the prompt if successful.

    public static void setDesiredCapacity(AutoScalingClient autoScalingClient, String groupName) {
        try {
            SetDesiredCapacityRequest capacityRequest = SetDesiredCapacityRequest.builder()
                    .autoScalingGroupName(groupName)
                    .desiredCapacity(2)
                    .build();

            autoScalingClient.setDesiredCapacity(capacityRequest);
            System.out.println("You have set the DesiredCapacity to 2");

        } catch (AutoScalingException e) {
            System.err.println(e.awsErrorDetails().errorMessage());
            System.exit(1);
        }
    }

suspend fun setDesiredCapacity(groupName: String) {
    val capacityRequest =
        SetDesiredCapacityRequest {
            autoScalingGroupName = groupName
            desiredCapacity = 2
        }

    AutoScalingClient { region = "us-east-1" }.use { autoScalingClient ->
        autoScalingClient.setDesiredCapacity(capacityRequest)
        println("You set the DesiredCapacity to 2")
    }
}

    public function setDesiredCapacity($autoScalingGroupName, $desiredCapacity)
    {
        return $this->autoScalingClient->setDesiredCapacity([
            'AutoScalingGroupName' => $autoScalingGroupName,
            'DesiredCapacity' => $desiredCapacity,
        ]);
    }

Example 1: This example sets the size of the specified Auto Scaling group.

Set-ASDesiredCapacity -AutoScalingGroupName my-asg -DesiredCapacity 2

Example 2: This example sets the size of the specified Auto Scaling group and waits for the cooldown period to complete before scaling to the new size.

Set-ASDesiredCapacity -AutoScalingGroupName my-asg -DesiredCapacity 2 -HonorCooldown $true

class AutoScalingWrapper:
    """Encapsulates Amazon EC2 Auto Scaling actions."""

    def __init__(self, autoscaling_client):
        """
        :param autoscaling_client: A Boto3 Amazon EC2 Auto Scaling client.
        """
        self.autoscaling_client = autoscaling_client


    def set_desired_capacity(self, group_name: str, capacity: int) -> None:
        """
        Sets the desired capacity of the group. Amazon EC2 Auto Scaling tries to keep the
        number of running instances equal to the desired capacity.

        :param group_name: The name of the group to update.
        :param capacity: The desired number of running instances.
        :return: None
        :raises ClientError: If there is an error setting the desired capacity.
        """
        try:
            self.autoscaling_client.set_desired_capacity(
                AutoScalingGroupName=group_name,
                DesiredCapacity=capacity,
                HonorCooldown=False,
            )
            logger.info(
                f"Successfully set desired capacity of {capacity} for Auto Scaling group '{group_name}'."
            )

        except ClientError as err:
            error_code = err.response["Error"]["Code"]
            logger.error(
                f"Failed to set desired capacity for Auto Scaling group '{group_name}'."
            )
            if error_code == "ScalingActivityInProgress":
                logger.error(
                    f"A scaling activity is currently in progress for the Auto Scaling group '{group_name}'. "
                    "Please wait for the activity to complete before attempting to set the desired capacity."
                )
            logger.error(f"Full error:\n\t{err}")
            raise

    pub async fn scale_desired_capacity(&self, capacity: i32) -> Result<(), ScenarioError> {
        // 7. SetDesiredCapacity: set desired capacity to 2.
        //   Wait for a second instance to launch.
        let update_group = self
            .autoscaling
            .set_desired_capacity()
            .auto_scaling_group_name(self.auto_scaling_group_name.clone())
            .desired_capacity(capacity)
            .send()
            .await;
        if let Err(err) = update_group {
            return Err(ScenarioError::new(
                format!("Failed to update group to desired capacity ({capacity}))").as_str(),
                &err,
            ));
        }
        Ok(())
    }