Use TerminateInstanceInAutoScalingGroup with an AWS SDK or CLI

    /// <summary>
    /// Terminate all instances in the Auto Scaling group in preparation for
    /// deleting the group.
    /// </summary>
    /// <param name="instanceId">The instance Id of the instance to terminate.</param>
    /// <returns>A Boolean value that indicates the success or failure of
    /// the operation.</returns>
    public async Task<bool> TerminateInstanceInAutoScalingGroupAsync(
        string instanceId)
    {
        var request = new TerminateInstanceInAutoScalingGroupRequest
        {
            InstanceId = instanceId,
            ShouldDecrementDesiredCapacity = false,
        };

        var response = await _amazonAutoScaling.TerminateInstanceInAutoScalingGroupAsync(request);

        if (response.HttpStatusCode == System.Net.HttpStatusCode.OK)
        {
            Console.WriteLine($"You have terminated the instance: {instanceId}");
            return true;
        }

        Console.WriteLine($"Could not terminate {instanceId}");
        return false;
    }

        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::TerminateInstanceInAutoScalingGroupRequest request;
        request.SetInstanceId(instanceIDs[instanceNumber - 1]);
        request.SetShouldDecrementDesiredCapacity(false);

        Aws::AutoScaling::Model::TerminateInstanceInAutoScalingGroupOutcome outcome =
                autoScalingClient.TerminateInstanceInAutoScalingGroup(request);

        if (outcome.IsSuccess()) {
            std::cout << "Waiting for EC2 instance with ID '"
                      << instanceIDs[instanceNumber - 1] << "' to terminate..."
                      << std::endl;
        }
        else {
            std::cerr << "Error with AutoScaling::TerminateInstanceInAutoScalingGroup. "
                      << outcome.GetError().GetMessage()
                      << std::endl;

        }

To terminate an instance in an Auto Scaling group

This example terminates the specified instance from the specified Auto Scaling group without updating the size of the group. Amazon EC2 Auto Scaling launches a replacement instance after the specified instance terminates.

aws autoscaling terminate-instance-in-auto-scaling-group \
    --instance-id i-061c63c5eb45f0416 \
    --no-should-decrement-desired-capacity

Output:

{
    "Activities": [
        {
            "ActivityId": "8c35d601-793c-400c-fcd0-f64a27530df7",
            "AutoScalingGroupName": "my-asg",
            "Description": "Terminating EC2 instance: i-061c63c5eb45f0416",
            "Cause": "",
            "StartTime": "2020-10-31T20:34:25.680Z",
            "StatusCode": "InProgress",
            "Progress": 0,
            "Details": "{\"Subnet ID\":\"subnet-6194ea3b\",\"Availability Zone\":\"us-west-2c\"}"
        }
    ]
}

    public static void terminateInstanceInAutoScalingGroup(AutoScalingClient autoScalingClient, String instanceId) {
        try {
            TerminateInstanceInAutoScalingGroupRequest request = TerminateInstanceInAutoScalingGroupRequest.builder()
                    .instanceId(instanceId)
                    .shouldDecrementDesiredCapacity(false)
                    .build();

            autoScalingClient.terminateInstanceInAutoScalingGroup(request);
            System.out.println("You have terminated instance " + instanceId);

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

suspend fun terminateInstanceInAutoScalingGroup(instanceIdVal: String) {
    val request =
        TerminateInstanceInAutoScalingGroupRequest {
            instanceId = instanceIdVal
            shouldDecrementDesiredCapacity = false
        }

    AutoScalingClient { region = "us-east-1" }.use { autoScalingClient ->
        autoScalingClient.terminateInstanceInAutoScalingGroup(request)
        println("You have terminated instance $instanceIdVal")
    }
}

    public function terminateInstanceInAutoScalingGroup(
        $instanceId,
        $shouldDecrementDesiredCapacity = true,
        $attempts = 0
    ) {
        try {
            return $this->autoScalingClient->terminateInstanceInAutoScalingGroup([
                'InstanceId' => $instanceId,
                'ShouldDecrementDesiredCapacity' => $shouldDecrementDesiredCapacity,
            ]);
        } catch (AutoScalingException $exception) {
            if ($exception->getAwsErrorCode() == "ScalingActivityInProgress" && $attempts < 5) {
                error_log("Cannot terminate an instance while it is still pending. Waiting then trying again.");
                sleep(5 * (1 + $attempts));
                return $this->terminateInstanceInAutoScalingGroup(
                    $instanceId,
                    $shouldDecrementDesiredCapacity,
                    ++$attempts
                );
            } else {
                throw $exception;
            }
        }
    }

Example 1: This example terminates the specified instance and decreases the desired capacity of its Auto Scaling group so that Auto Scaling does not launch a replacement instance.

Stop-ASInstanceInAutoScalingGroup -InstanceId i-93633f9b -ShouldDecrementDesiredCapacity $true

Output:

ActivityId           : 2e40d9bd-1902-444c-abf3-6ea0002efdc5
AutoScalingGroupName :
Cause                : At 2015-11-22T16:09:03Z instance i-93633f9b was taken out of service in response to a user 
                       request, shrinking the capacity from 2 to 1.
Description          : Terminating EC2 instance: i-93633f9b
Details              : {"Availability Zone":"us-west-2b","Subnet ID":"subnet-5264e837"}
EndTime              : 
Progress             : 0
StartTime            : 11/22/2015 8:09:03 AM
StatusCode           : InProgress
StatusMessage        :

Example 2: This example terminates the specified instance without decreasing the desired capacity of its Auto Scaling group. Auto Scaling launches a replacement instance.

Stop-ASInstanceInAutoScalingGroup -InstanceId i-93633f9b -ShouldDecrementDesiredCapacity $false

Output:

ActivityId           : 2e40d9bd-1902-444c-abf3-6ea0002efdc5
AutoScalingGroupName :
Cause                : At 2015-11-22T16:09:03Z instance i-93633f9b was taken out of service in response to a user 
                       request.
Description          : Terminating EC2 instance: i-93633f9b
Details              : {"Availability Zone":"us-west-2b","Subnet ID":"subnet-5264e837"}
EndTime              : 
Progress             : 0
StartTime            : 11/22/2015 8:09:03 AM
StatusCode           : InProgress
StatusMessage        :

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 terminate_instance(
        self, instance_id: str, decrease_capacity: bool
    ) -> Dict[str, Any]:
        """
        Stops an instance.

        :param instance_id: The ID of the instance to stop.
        :param decrease_capacity: Specifies whether to decrease the desired capacity
                                  of the group. When passing True for this parameter,
                                  you can stop an instance without having a replacement
                                  instance start when the desired capacity threshold is
                                  crossed.
        :return: A dictionary containing details of the scaling activity that occurs
                 in response to this action.
        :raises ClientError: If there is an error terminating the instance.
        """
        try:
            response = self.autoscaling_client.terminate_instance_in_auto_scaling_group(
                InstanceId=instance_id, ShouldDecrementDesiredCapacity=decrease_capacity
            )
            logger.info(f"Successfully terminated instance {instance_id}.")
            return response["Activity"]

        except ClientError as err:
            error_code = err.response["Error"]["Code"]
            logger.error(f"Failed to terminate instance {instance_id}.")
            if error_code == "ScalingActivityInProgress":
                logger.error(
                    "A scaling activity is currently in progress for the Auto Scaling group "
                    f"associated with instance '{instance_id}'. "
                    "Please wait for the activity to complete before attempting to terminate the instance."
                )
            elif error_code == "ResourceInUse":
                logger.error(
                    f"The instance '{instance_id}' or an associated resource is currently in use "
                    "and cannot be terminated. "
                    "Ensure the instance is not involved in any ongoing processes and try again."
                )
            logger.error(f"Full error:\n\t{err}")
            raise

    pub async fn terminate_some_instance(&self) -> Result<(), ScenarioError> {
        // Retrieve a list of instances in the auto scaling group.
        let auto_scaling_group = self.get_group().await?;
        let instances = auto_scaling_group.instances();
        // Or use other logic to find an instance to terminate.
        let instance = instances.first();
        if let Some(instance) = instance {
            let instance_id = if let Some(instance_id) = instance.instance_id() {
                instance_id
            } else {
                return Err(ScenarioError::with("Missing instance id"));
            };
            let termination = self
                .ec2
                .terminate_instances()
                .instance_ids(instance_id)
                .send()
                .await;
            if let Err(err) = termination {
                Err(ScenarioError::new(
                    "There was a problem terminating an instance",
                    &err,
                ))
            } else {
                Ok(())
            }
        } else {
            Err(ScenarioError::with("There was no instance to terminate"))
        }
    }

    async fn get_group(&self) -> Result<AutoScalingGroup, ScenarioError> {
        let describe_auto_scaling_groups = self
            .autoscaling
            .describe_auto_scaling_groups()
            .auto_scaling_group_names(self.auto_scaling_group_name.clone())
            .send()
            .await;

        if let Err(err) = describe_auto_scaling_groups {
            return Err(ScenarioError::new(
                format!(
                    "Failed to get status of autoscaling group {}",
                    self.auto_scaling_group_name.clone()
                )
                .as_str(),
                &err,
            ));
        }

        let describe_auto_scaling_groups_output = describe_auto_scaling_groups.unwrap();
        let auto_scaling_groups = describe_auto_scaling_groups_output.auto_scaling_groups();
        let auto_scaling_group = auto_scaling_groups.first();

        if auto_scaling_group.is_none() {
            return Err(ScenarioError::with(format!(
                "Could not find autoscaling group {}",
                self.auto_scaling_group_name.clone()
            )));
        }

        Ok(auto_scaling_group.unwrap().clone())
    }