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Auto Scaling for Instances

Red Hat OpenStack Platform 12

Configure Auto Scaling in Red Hat OpenStack Platform

OpenStack Documentation Team

Abstract

Automatically scale out your Compute instances in response to system usage.

Chapter 1. About This Guide

Warning

Red Hat is currently reviewing the information and procedures provided in this guide for this release.

This document is based on the Red Hat OpenStack Platform 10 document, available at https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/?version=10.

If you require assistance for Red Hat OpenStack Platform 11, please contact Red Hat support.

Chapter 2. Configure Auto Scaling for Compute Instances

This guide describes how to automatically scale out your Compute instances in response to heavy system usage. By using pre-defined rules that consider factors such as CPU or memory usage, you can configure Orchestration (heat) to add and remove additional instances automatically, when they are needed.

2.1. Architectural Overview

2.1.1. Orchestration

The core component providing automatic scaling is Orchestration (heat). Orchestration allows you to define rules using human-readable YAML templates. These rules are applied to evaluate system load based on Telemetry data to find out whether there is need to add more instances into the stack. Once the load has dropped, Orchestration can automatically remove the unused instances again.

2.1.2. Telemetry

Telemetry does performance monitoring of your OpenStack environment, collecting data on CPU, storage, and memory utilization for instances and physical hosts. Orchestration templates examine Telemetry data to assess whether any pre-defined action should start.

2.1.3. Key Terms

  • Stack - A stack stands for all the resources necessary to operate an application. It can be as simple as a single instance and its resources, or as complex as multiple instances with all the resource dependencies that comprise a multi-tier application.
  • Templates - YAML scripts that define a series of tasks for Heat to execute. For example, it is preferable to use separate templates for certain functions:

    • Template File - This is where you define thresholds that Telemetry should respond to, and define the auto scaling group.
    • Environment File - Defines the build information for your environment: which flavor and image to use, how the virtual network should be configured, and what software should be installed.

2.2. Example: Auto Scaling Based on CPU Usage

In this example, Orchestration examines Telemetry data, and automatically increases the number of instances in response to high CPU usage. A stack template and environment template are created to define the needed rules and subsequent configuration. This example makes use of existing resources (such as networks), and uses names that are likely to differ in your own environment.

  1. Create the environment template, describing the instance flavor, networking configuration, and image type and save it in the template /home/<user>/stacks/example1/cirros.yaml file. Please, replace the <user> variable with a real user name:

    heat_template_version: 2016-10-14
    description: Template to spawn an cirros instance.
    
    parameters:
      metadata:
        type: json
      image:
        type: string
        description: image used to create instance
        default: cirros
      flavor:
        type: string
        description: instance flavor to be used
        default: m1.tiny
      key_name:
        type: string
        description: keypair to be used
        default: mykeypair
      network:
        type: string
        description: project network to attach instance to
        default: internal1
      external_network:
        type: string
        description: network used for floating IPs
        default: external_network
    
    resources:
      server:
        type: OS::Nova::Server
        properties:
          block_device_mapping:
            - device_name: vda
              delete_on_termination: true
              volume_id: { get_resource: volume }
          flavor: {get_param: flavor}
          key_name: {get_param: key_name}
          metadata: {get_param: metadata}
          networks:
            - port: { get_resource: port }
    
      port:
        type: OS::Neutron::Port
        properties:
          network: {get_param: network}
          security_groups:
            - default
    
      floating_ip:
        type: OS::Neutron::FloatingIP
        properties:
          floating_network: {get_param: external_network}
    
      floating_ip_assoc:
        type: OS::Neutron::FloatingIPAssociation
        properties:
          floatingip_id: { get_resource: floating_ip }
          port_id: { get_resource: port }
    
      volume:
        type: OS::Cinder::Volume
        properties:
          image: {get_param: cirros}
          size: 1
  2. Register the Orchestration resource in ~/stacks/example1/environment.yaml:

    resource_registry:
    
        "OS::Nova::Server::Cirros": ~/stacks/example1/cirros.yaml
  3. Create the stack template, describing the CPU thresholds to watch for, and how many instances should be added. An instance group is also created, defining the minimum and maximum number of instances that can participate in this template.

    Note

    The granularity parameter needs to be set according to gnocchi cpu_util metric granularity. For more information, refer to this solution article.

    Save the following values in ~/stacks/example1/template.yaml:

    heat_template_version: 2016-10-14
    description: Example auto scale group, policy and alarm
    resources:
      scaleup_group:
        type: OS::Heat::AutoScalingGroup
        properties:
          cooldown: 300
          desired_capacity: 1
          max_size: 3
          min_size: 1
          resource:
            type: OS::Nova::Server::Cirros
            properties:
              metadata: {"metering.server_group": {get_param: "OS::stack_id"}}
    
      scaleup_policy:
        type: OS::Heat::ScalingPolicy
        properties:
          adjustment_type: change_in_capacity
          auto_scaling_group_id: { get_resource: scaleup_group }
          cooldown: 300
          scaling_adjustment: 1
    
      scaledown_policy:
        type: OS::Heat::ScalingPolicy
        properties:
          adjustment_type: change_in_capacity
          auto_scaling_group_id: { get_resource: scaleup_group }
          cooldown: 300
          scaling_adjustment: -1
    
      cpu_alarm_high:
        type: OS::Aodh::GnocchiAggregationByResourcesAlarm
        properties:
          description: Scale up if CPU > 80%
          metric: cpu_util
          aggregation_method: mean
          granularity: 300
          evaluation_periods: 1
          threshold: 80
          resource_type: instance
          comparison_operator: gt
          alarm_actions:
            - str_replace:
                template: trust+url
                params:
                  url: {get_attr: [scaleup_policy, signal_url]}
          query:
            str_replace:
              template: '{"=": {"server_group": "stack_id"}}'
              params:
                stack_id: {get_param: "OS::stack_id"}
    
      cpu_alarm_low:
        type: OS::Aodh::GnocchiAggregationByResourcesAlarm
        properties:
          metric: cpu_util
          aggregation_method: mean
          granularity: 300
          evaluation_periods: 1
          threshold: 5
          resource_type: instance
          comparison_operator: lt
          alarm_actions:
            - str_replace:
                template: trust+url
                params:
                  url: {get_attr: [scaledown_policy, signal_url]}
          query:
            str_replace:
              template: '{"=": {"server_group": "stack_id"}}'
              params:
                stack_id: {get_param: "OS::stack_id"}
    
    outputs:
      scaleup_policy_signal_url:
        value: {get_attr: [scaleup_policy, signal_url]}
    
      scaledown_policy_signal_url:
        value: {get_attr: [scaledown_policy, signal_url]}
  4. Run the following OpenStack command to build the environment and deploy the instance:

    $ openstack stack create  -t template.yaml -e environment.yaml example
    +---------------------+--------------------------------------------+
    | Field               | Value                                      |
    +---------------------+--------------------------------------------+
    | id                  | 248a98bb-f56e-4934-a281-fffde62d78d8       |
    | stack_name          | example                                   |
    | description         | Example auto scale group, policy and alarm |
    | creation_time       | 2017-03-06T15:00:29Z                       |
    | updated_time        | None                                       |
    | stack_status        | CREATE_IN_PROGRESS                         |
    | stack_status_reason | Stack CREATE started                       |
    +---------------------+--------------------------------------------+
  5. Orchestration will create the stack and launch a defined minimum number of cirros instances, as defined in the min_size parameter of the scaleup_group definition. Verify that the instances were created successfully:

    $ openstack server list
    +--------------------------------------+-------------------------------------------------------+--------+------------+-------------+-------------------------------------+
    | ID                                   | Name                                                  | Status | Task State | Power State | Networks                            |
    +--------------------------------------+-------------------------------------------------------+--------+------------+-------------+-------------------------------------+
    | e1524f65-5be6-49e4-8501-e5e5d812c612 | ex-3gax-5f3a4og5cwn2-png47w3u2vjd-server-vaajhuv4mj3j | ACTIVE | -          | Running     | internal1=10.10.10.9, 192.168.122.8 |
    +--------------------------------------+-------------------------------------------------------+--------+------------+-------------+-------------------------------------+
  6. Orchestration also creates two cpu alarms which are used to trigger scale-up or scale-down events, as defined in cpu_alarm_high and cpu_alarm_low. Verify that the triggers exist:

    $ openstack alarm list
    +--------------------------------------+--------------------------------------------+-------------------------------------+-------------------+----------+---------+
    | alarm_id                             | type                                       | name                                | state             | severity | enabled |
    +--------------------------------------+--------------------------------------------+-------------------------------------+-------------------+----------+---------+
    | 022f707d-46cc-4d39-a0b2-afd2fc7ab86a | gnocchi_aggregation_by_resources_threshold | example-cpu_alarm_high-odj77qpbld7j | insufficient data | low      | True    |
    | 46ed2c50-e05a-44d8-b6f6-f1ebd83af913 | gnocchi_aggregation_by_resources_threshold | example-cpu_alarm_low-m37jvnm56x2t  | insufficient data | low      | True    |
    +--------------------------------------+--------------------------------------------+-------------------------------------+-------------------+----------+---------+

2.2.1. Test Automatic Scaling Up Instances

Orchestration can scale instances automatically based on the cpu_alarm_high threshold definition. Once the CPU utilization reaches a value defined in the threshold parameter, another instance is started to balance the load. The threshold value in the above template.yaml file is set to 80%.

  1. Login to the instance and run several dd commands to generate the load:

    $ ssh -i ~/mykey.pem cirros@192.168.122.8
    $ sudo dd if=/dev/zero of=/dev/null &
    $ sudo dd if=/dev/zero of=/dev/null &
    $ sudo dd if=/dev/zero of=/dev/null &
  2. Having run the dd commands, you can expect to have 100% CPU utilization in the cirros instance. Verify that the alarm has been triggered:

    $ openstack alarm list
    +--------------------------------------+--------------------------------------------+-------------------------------------+-------+----------+---------+
    | alarm_id                             | type                                       | name                                | state | severity | enabled |
    +--------------------------------------+--------------------------------------------+-------------------------------------+-------+----------+---------+
    | 022f707d-46cc-4d39-a0b2-afd2fc7ab86a | gnocchi_aggregation_by_resources_threshold | example-cpu_alarm_high-odj77qpbld7j | alarm | low      | True    |
    | 46ed2c50-e05a-44d8-b6f6-f1ebd83af913 | gnocchi_aggregation_by_resources_threshold | example-cpu_alarm_low-m37jvnm56x2t  | ok    | low      | True    |
    +--------------------------------------+--------------------------------------------+-------------------------------------+-------+----------+---------+
  3. After some time (approximately 60 seconds), Orchestration will start another instance and add it into the group. You can verify this with the nova list command:

    $ openstack server list
    +--------------------------------------+-------------------------------------------------------+--------+------------+-------------+---------------------------------------+
    | ID                                   | Name                                                  | Status | Task State | Power State | Networks                              |
    +--------------------------------------+-------------------------------------------------------+--------+------------+-------------+---------------------------------------+
    | 477ee1af-096c-477c-9a3f-b95b0e2d4ab5 | ex-3gax-4urpikl5koff-yrxk3zxzfmpf-server-2hde4tp4trnk | ACTIVE | -          | Running     | internal1=10.10.10.13, 192.168.122.17 |
    | e1524f65-5be6-49e4-8501-e5e5d812c612 | ex-3gax-5f3a4og5cwn2-png47w3u2vjd-server-vaajhuv4mj3j | ACTIVE | -          | Running     | internal1=10.10.10.9, 192.168.122.8   |
    +--------------------------------------+-------------------------------------------------------+--------+------------+-------------+---------------------------------------+
  4. After another short period, you will observe that Orchestration has auto scaled again to three instances. The configuration is set to three instances maximally, so it will not scale any higher (the scaleup_group definition: max_size). Again, you can verify that with the above mentioned command:

    $ openstack server list
    +--------------------------------------+-------------------------------------------------------+--------+------------+-------------+---------------------------------------+
    | ID                                   | Name                                                  | Status | Task State | Power State | Networks                              |
    +--------------------------------------+-------------------------------------------------------+--------+------------+-------------+---------------------------------------+
    | 477ee1af-096c-477c-9a3f-b95b0e2d4ab5 | ex-3gax-4urpikl5koff-yrxk3zxzfmpf-server-2hde4tp4trnk | ACTIVE | -          | Running     | internal1=10.10.10.13, 192.168.122.17 |
    | e1524f65-5be6-49e4-8501-e5e5d812c612 | ex-3gax-5f3a4og5cwn2-png47w3u2vjd-server-vaajhuv4mj3j | ACTIVE | -          | Running     | internal1=10.10.10.9, 192.168.122.8   |
    | 6c88179e-c368-453d-a01a-555eae8cd77a | ex-3gax-fvxz3tr63j4o-36fhftuja3bw-server-rhl4sqkjuy5p | ACTIVE | -          | Running     | internal1=10.10.10.5, 192.168.122.5   |
    +--------------------------------------+-------------------------------------------------------+--------+------------+-------------+---------------------------------------+

2.2.2. Automatically Scaling Down Instances

Orchestration can also automatically scale down instances based on the cpu_alarm_low threshold. In this example, the instances are scaled down once CPU utilization is below 5%.

  1. Terminate the running dd processes and you will observe Orchestration begin to scale the instances back down.

    $ killall dd
  2. Stopping the dd processes causes the cpu_alarm_low event to trigger. As a result, Orchestration begins to automatically scale down and remove the instances. Verify, that the corresponding alarm has been triggered.

    $ openstack alarm list
    +--------------------------------------+--------------------------------------------+-------------------------------------+-------+----------+---------+
    | alarm_id                             | type                                       | name                                | state | severity | enabled |
    +--------------------------------------+--------------------------------------------+-------------------------------------+-------+----------+---------+
    | 022f707d-46cc-4d39-a0b2-afd2fc7ab86a | gnocchi_aggregation_by_resources_threshold | example-cpu_alarm_high-odj77qpbld7j | ok    | low      | True    |
    | 46ed2c50-e05a-44d8-b6f6-f1ebd83af913 | gnocchi_aggregation_by_resources_threshold | example-cpu_alarm_low-m37jvnm56x2t  | alarm | low      | True    |
    +--------------------------------------+--------------------------------------------+-------------------------------------+-------+----------+---------+

    After a few minutes, Orchestration continually reduce the number of instances to the minimum value defined in the min_size parameter of the scaleup_group definition. In this scenario, the min_size parameter is set to 1.

2.2.3. Troubleshooting the setup

If your environment is not working properly, you can look for errors in the log files and history records.

  1. To get information on state transitions, you can list the stack event records:

    $ openstack stack event list example
    2017-03-06 11:12:43Z [example]: CREATE_IN_PROGRESS  Stack CREATE started
    2017-03-06 11:12:43Z [example.scaleup_group]: CREATE_IN_PROGRESS  state changed
    2017-03-06 11:13:04Z [example.scaleup_group]: CREATE_COMPLETE  state changed
    2017-03-06 11:13:04Z [example.scaledown_policy]: CREATE_IN_PROGRESS  state changed
    2017-03-06 11:13:05Z [example.scaleup_policy]: CREATE_IN_PROGRESS  state changed
    2017-03-06 11:13:05Z [example.scaledown_policy]: CREATE_COMPLETE  state changed
    2017-03-06 11:13:05Z [example.scaleup_policy]: CREATE_COMPLETE  state changed
    2017-03-06 11:13:05Z [example.cpu_alarm_low]: CREATE_IN_PROGRESS  state changed
    2017-03-06 11:13:05Z [example.cpu_alarm_high]: CREATE_IN_PROGRESS  state changed
    2017-03-06 11:13:06Z [example.cpu_alarm_low]: CREATE_COMPLETE  state changed
    2017-03-06 11:13:07Z [example.cpu_alarm_high]: CREATE_COMPLETE  state changed
    2017-03-06 11:13:07Z [example]: CREATE_COMPLETE  Stack CREATE completed successfully
    2017-03-06 11:19:34Z [example.scaleup_policy]: SIGNAL_COMPLETE  alarm state changed from alarm to alarm (Remaining as alarm due to 1 samples outside threshold, most recent: 95.4080102993)
    2017-03-06 11:25:43Z [example.scaleup_policy]: SIGNAL_COMPLETE  alarm state changed from alarm to alarm (Remaining as alarm due to 1 samples outside threshold, most recent: 95.8869217299)
    2017-03-06 11:33:25Z [example.scaledown_policy]: SIGNAL_COMPLETE  alarm state changed from ok to alarm (Transition to alarm due to 1 samples outside threshold, most recent: 2.73931707966)
    2017-03-06 11:39:15Z [example.scaledown_policy]: SIGNAL_COMPLETE  alarm state changed from alarm to alarm (Remaining as alarm due to 1 samples outside threshold, most recent: 2.78110858552)
  2. To read the alarm history log:

    $ openstack alarm-history show 022f707d-46cc-4d39-a0b2-afd2fc7ab86a
    +----------------------------+------------------+-----------------------------------------------------------------------------------------------------+--------------------------------------+
    | timestamp                  | type             | detail                                                                                              | event_id                             |
    +----------------------------+------------------+-----------------------------------------------------------------------------------------------------+--------------------------------------+
    | 2017-03-06T11:32:35.510000 | state transition | {"transition_reason": "Transition to ok due to 1 samples inside threshold, most recent:             | 25e0e70b-3eda-466e-abac-42d9cf67e704 |
    |                            |                  | 2.73931707966", "state": "ok"}                                                                      |                                      |
    | 2017-03-06T11:17:35.403000 | state transition | {"transition_reason": "Transition to alarm due to 1 samples outside threshold, most recent:         | 8322f62c-0d0a-4dc0-9279-435510f81039 |
    |                            |                  | 95.0964497325", "state": "alarm"}                                                                   |                                      |
    | 2017-03-06T11:15:35.723000 | state transition | {"transition_reason": "Transition to ok due to 1 samples inside threshold, most recent:             | 1503bd81-7eba-474e-b74e-ded8a7b630a1 |
    |                            |                  | 3.59330523447", "state": "ok"}                                                                      |                                      |
    | 2017-03-06T11:13:06.413000 | creation         | {"alarm_actions": ["trust+http://fca6e27e3d524ed68abdc0fd576aa848:delete@192.168.122.126:8004/v1/fd | 224f15c0-b6f1-4690-9a22-0c1d236e65f6 |
    |                            |                  | 1c345135be4ee587fef424c241719d/stacks/example/d9ef59ed-b8f8-4e90-bd9b-                              |                                      |
    |                            |                  | ae87e73ef6e2/resources/scaleup_policy/signal"], "user_id": "a85f83b7f7784025b6acdc06ef0a8fd8",      |                                      |
    |                            |                  | "name": "example-cpu_alarm_high-odj77qpbld7j", "state": "insufficient data", "timestamp":           |                                      |
    |                            |                  | "2017-03-06T11:13:06.413455", "description": "Scale up if CPU > 80%", "enabled": true,              |                                      |
    |                            |                  | "state_timestamp": "2017-03-06T11:13:06.413455", "rule": {"evaluation_periods": 1, "metric":        |                                      |
    |                            |                  | "cpu_util", "aggregation_method": "mean", "granularity": 300, "threshold": 80.0, "query": "{\"=\":   |                                      |
    |                            |                  | {\"server_group\": \"d9ef59ed-b8f8-4e90-bd9b-ae87e73ef6e2\"}}", "comparison_operator": "gt",        |                                      |
    |                            |                  | "resource_type": "instance"}, "alarm_id": "022f707d-46cc-4d39-a0b2-afd2fc7ab86a",                   |                                      |
    |                            |                  | "time_constraints": [], "insufficient_data_actions": null, "repeat_actions": true, "ok_actions":    |                                      |
    |                            |                  | null, "project_id": "fd1c345135be4ee587fef424c241719d", "type":                                     |                                      |
    |                            |                  | "gnocchi_aggregation_by_resources_threshold", "severity": "low"}                                    |                                      |
    +----------------------------+------------------+-----------------------------------------------------------------------------------------------------+-------------------------------------
  3. To see the records of scale-out or scale-down operations that heat collects for the existing stack, you can use awk to parse the heat-engine.log:

    $ awk '/Stack UPDATE started/,/Stack CREATE completed successfully/ {print $0}' /var/log/heat/heat-engine.log
  4. To see the aodh related information, examine the evaluator.log:

    $ grep -i alarm /var/log/aodh/evaluator.log | grep -i transition

2.3. Example: Auto Scaling Applications

The functionality described earlier can also be used to scale up applications; for example, a dynamic web page that be served by one of multiple instances running at a time. In this case, neutron can be configured to provide Load Balancing-as-a-Service, which works to evenly distribute traffic among instances.

In the following example, Orchestration again examines Telemetry data and increases the number of instances if high CPU usage is detected, or decreases the number of instances if CPU usage returns below a set value.

  1. Create the template describing the properties of the load-balancer environment. Enter the following values in ~/stacks/example2/lb-env.yaml:

    heat_template_version: 2014-10-16
    description: A load-balancer server
    parameters:
      image:
        type: string
        description: Image used for servers
      key_name:
        type: string
        description: SSH key to connect to the servers
      flavor:
        type: string
        description: flavor used by the servers
      pool_id:
        type: string
        description: Pool to contact
      user_data:
        type: string
        description: Server user_data
      metadata:
        type: json
      network:
        type: string
        description: Network used by the server
    
    resources:
      server:
        type: OS::Nova::Server
        properties:
          flavor: {get_param: flavor}
          image: {get_param: image}
          key_name: {get_param: key_name}
          metadata: {get_param: metadata}
          user_data: {get_param: user_data}
          networks:
            - port: { get_resource: port }
    
      member:
        type: OS::Neutron::PoolMember
        properties:
          pool_id: {get_param: pool_id}
          address: {get_attr: [server, first_address]}
          protocol_port: 80
    
      port:
        type: OS::Neutron::Port
        properties:
          network: {get_param: network}
          security_groups:
            - base
    
    outputs:
      server_ip:
        description: IP Address of the load-balanced server.
        value: { get_attr: [server, first_address] }
      lb_member:
        description: LB member details.
        value: { get_attr: [member, show] }
  2. Create another template for the instances that will be running the web application. The following template creates a load balancer and uses the existing networks. Be sure to replace the parameters according to your environment, and save the template in a file such as ~/stacks/example2/lb-webserver-rhel7.yaml:

    heat_template_version: 2014-10-16
    description: AutoScaling RHEL 7 Web Application
    parameters:
      image:
        type: string
        description: Image used for servers
        default: RHEL 7
      key_name:
        type: string
        description: SSH key to connect to the servers
        default: admin
      flavor:
        type: string
        description: flavor used by the web servers
        default: m2.tiny
      network:
        type: string
        description: Network used by the server
        default: private
      subnet_id:
        type: string
        description: subnet on which the load balancer will be located
        default: 9daa6b7d-e647-482a-b387-dd5f855b88ef
      external_network_id:
        type: string
        description: UUID of a Neutron external network
        default: db17c885-77fa-45e8-8647-dbb132517960
    
    resources:
      webserver:
        type: OS::Heat::AutoScalingGroup
        properties:
          min_size: 1
          max_size: 3
          cooldown: 60
          desired_capacity: 1
          resource:
            type: file:///etc/heat/templates/lb-env.yaml
            properties:
              flavor: {get_param: flavor}
              image: {get_param: image}
              key_name: {get_param: key_name}
              network: {get_param: network}
              pool_id: {get_resource: pool}
              metadata: {"metering.stack": {get_param: "OS::stack_id"}}
              user_data:
                str_replace:
                  template: |
                    #!/bin/bash -v
    
                    yum -y install httpd php
                    systemctl enable httpd
                    systemctl start httpd
                    cat <<EOF > /var/www/html/hostname.php
                    <?php echo "Hello, My name is " . php_uname('n'); ?>
                    EOF
                  params:
                    hostip: 192.168.122.70
                    fqdn: sat6.example.com
                    shortname: sat6
    
      web_server_scaleup_policy:
        type: OS::Heat::ScalingPolicy
        properties:
          adjustment_type: change_in_capacity
          auto_scaling_group_id: {get_resource: webserver}
          cooldown: 60
          scaling_adjustment: 1
    
      web_server_scaledown_policy:
        type: OS::Heat::ScalingPolicy
        properties:
          adjustment_type: change_in_capacity
          auto_scaling_group_id: {get_resource: webserver}
          cooldown: 60
          scaling_adjustment: -1
    
      cpu_alarm_high:
        type: OS::Aodh::GnocchiAggregationByResourcesAlarm
        properties:
          description: Scale-up if the average CPU > 95% for 1 minute
          meter_name: cpu_util
          statistic: avg
          period: 60
          evaluation_periods: 1
          threshold: 95
          alarm_actions:
            - str_replace:
                template: trust+url
                params:
                    url: {get_attr: [server_scaleup_policy, signal_url]}
          matching_metadata: {'metadata.user_metadata.stack': {get_param: "OS::stack_id"}}
          comparison_operator: gt
    
      cpu_alarm_low:
        type: OS::Aodh::GnocchiAggregationByResourcesAlarm
        properties:
          description: Scale-down if the average CPU < 15% for 1 minute
          meter_name: cpu_util
          statistic: avg
          period: 60
          evaluation_periods: 1
          threshold: 15
          alarm_actions:
            - str_replace:
                template: trust+url
                params:
                    url: {get_attr: [server_scaleup_policy, signal_url]}
          matching_metadata: {'metadata.user_metadata.stack': {get_param: "OS::stack_id"}}
          comparison_operator: lt
    
      monitor:
        type: OS::Neutron::HealthMonitor
        properties:
          type: TCP
          delay: 5
          max_retries: 5
          timeout: 5
    
      pool:
        type: OS::Neutron::Pool
        properties:
          protocol: HTTP
          monitors: [{get_resource: monitor}]
          subnet_id: {get_param: subnet_id}
          lb_method: ROUND_ROBIN
          vip:
            protocol_port: 80
    
      lb:
        type: OS::Neutron::LoadBalancer
        properties:
          protocol_port: 80
          pool_id: {get_resource: pool}
    
      lb_floating:
        type: OS::Neutron::FloatingIP
        properties:
          floating_network_id: {get_param: external_network_id}
          port_id: {get_attr: [pool, vip, port_id]}
    
    outputs:
      scale_up_url:
        description: >
          This URL is the webhook to scale up the autoscaling group.  You
          can invoke the scale-up operation by doing an HTTP POST to this
          URL; no body nor extra headers are needed.
        value: {get_attr: [web_server_scaleup_policy, alarm_url]}
      scale_dn_url:
        description: >
          This URL is the webhook to scale down the autoscaling group.
          You can invoke the scale-down operation by doing an HTTP POST to
          this URL; no body nor extra headers are needed.
        value: {get_attr: [web_server_scaledown_policy, alarm_url]}
      pool_ip_address:
        value: {get_attr: [pool, vip, address]}
        description: The IP address of the load balancing pool
      website_url:
        value:
          str_replace:
            template: http://serviceip/hostname.php
            params:
              serviceip: { get_attr: [lb_floating, floating_ip_address] }
        description: >
          This URL is the "external" URL that can be used to access the
          website.
      ceilometer_query:
        value:
          str_replace:
            template: >
              ceilometer statistics -m cpu_util
              -q metadata.user_metadata.stack=stackval -p 60 -a avg
            params:
              stackval: { get_param: "OS::stack_id" }
        description: >
          This is a Ceilometer query for statistics on the cpu_util meter
          Samples about OS::Nova::Server instances in this stack.  The -q
          parameter selects Samples according to the subject's metadata.
          When a VM's metadata includes an item of the form metering.X=Y,
          the corresponding Ceilometer resource has a metadata item of the
          form user_metadata.X=Y and samples about resources so tagged can
          be queried with a Ceilometer query term of the form
          metadata.user_metadata.X=Y.  In this case the nested stacks give
          their VMs metadata that is passed as a nested stack parameter,
          and this stack passes a metadata of the form metering.stack=Y,
          where Y is this stack's ID.
  3. Update the Telemetry collection interval. By default, Telemetry polls instances every 10 minutes for CPU data. For this example, change the interval to 60 seconds in /etc/ceilometer/pipeline.yaml:

    - name: cpu_source
    interval: 60
    meters:
    - "cpu"
    sinks:
    - cpu_sink
    Note

    A polling period of 60 seconds is not recommended for production environments, as a higher polling interval can result in increased load on the control plane.

  4. Restart all OpenStack ceilometer services to apply the updated Telemetry setting:

    # systemctl restart openstack-ceilometer*
  5. Run the Orchestration scripts. This will build the environment and use the template to deploy the instance:

    # heat stack-create webfarm -f /root/lb-webserver-rhel7.yaml

    Replace /root/lb-webserver-rhel7.yaml with the actual path and file name.

You can monitor the creation of the stack in Dashboard under Orchestration → Stacks → Webfarm. Once the stack has been created, you are presented with multiple useful pieces of information, notably:

  • URLs that you can use to trigger manual scale-up or scale-down events.
  • The floating IP address, which is the IP address of the website.
  • The Telemetry command which shows the CPU load for the whole stack, and which you can use to check whether the scaling is working as expected.

This is what the page looks like in Dashboard:

heat stack output

Open Network → Load Balancers to view the load balancer:

load balancer

Click Members. This page displays the members of the load balancing pool; these are the instances to which the website traffic can be distributed. Note that a member will not have the Active status until the corresponding instance has been created, and Apache has been installed and configured.

When the web server has started, the instance is visible as an active member of the load balancer:

load balancer member active

You are now able to access the web application at http://IP/hostname.php. You can expect to see output similar to the following:

Hello, My name is we-zrwm-t4ezkpx34gxu-qbg5d7dqbc4j-server-mzdvigk2jugl

You can now view the stack’s CPU performance data by running the Telemetry command from the stack overview in Dashboard. The command looks like the following:

# ceilometer statistics -m cpu_util -q metadata.user_metadata.stack=8f86c3d5-15cf-4a64-b9e8-70215498c046 -p 60 -a avg

2.3.1. Test Auto Scaling Applications

To manually trigger application scaling, use the REST scale-up URL from the stack overview in Dashboard, or generate load by running a resource-intensive command on the initially deployed instance.

  • To use the REST API, you need a tool which can perform HTTP POST requests, such as the REST Easy Firefox add on or curl. Copy the scale-up URL and either paste it into the REST Easy form:

    scale up

    Or use it as a parameter on the curl command line:

    $ curl -X POST "scale-up URL"
  • To artificially generate load, allocate a floating IP to the instance, log in to it with SSH, and run a command which will keep the CPU busy. For example:

    $ dd if=/dev/zero of=/dev/null &
    Important

    Check whether CPU usage is above 95%, for example, using the top command. If the CPU usage is not sufficiently high, run the dd command multiple times in parallel, or use another method to keep the CPU busy.

The next time Telemetry collects CPU data from the stack, the scale-up event will trigger and appear at Orchestration → Stacks → Webfarm → Events. A new web server instance will be created and added to the load balancer. When this is done, the instance becomes active, and you will notice that the website URL is routed through the load balancer to both instances in the stack.

Note

The creation can take several minutes because the instance must be initialized, Apache installed and configured, and the application deployed. This is monitored by HAProxy, which ensures that the website is available on the instance before it is marked as active.

This is what the list of members of the load balancing pool looks like in the Dashboard while the new instance is being created:

scale up load balancer

Important

The average CPU usage of the instances in the heat stack is taken into account when deciding whether or not an additional instance gets created. Because the second instance will most likely have normal CPU usage, it will balance out the first instance. However, if the second instance becomes busy as well and the average CPU usage of the first and second instance exceeds 95%, another (third) instance will be created.

2.3.2. Automatically Scaling Down Applications

This is similar to Section 2.2.2, “Automatically Scaling Down Instances” in that the scale-down policy is triggered when the average CPU usage for the stack drops below a predefined value, which is 15% in the example described in Section 2.3.1, “Test Auto Scaling Applications”. In addition, when an instance is removed from the stack this way, it is also automatically removed from the load balancer. The website traffic is then automatically distributed among the rest of the instances.

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