When you operate the cloud day-to-day, you can define and create cloud resources and use telemetry services to collect data about cloud resource usage, so you can automatically scale instances in response to workload demand and resource availability.

You control automatic instance scaling with the following telemetry components:

• Telemetry service (ceilometer) for data collection.
• The time-series database service, Prometheus, for metrics data storage.
• The Alarming service (aodh) to trigger actions based on rules against metrics or event data.

Review the following terms before you start to configure autoscaling:

• Stack - A stack stands for all the resources necessary to operate an application. It can be a single instance and its resources or multiple instances with all the resource dependencies that comprise a multitiered application.
• Templates - YAML scripts that define a series of tasks for Orchestration (heat) to run. For example, it is preferable to use separate templates for certain functions:
  • Template file - This is where you define thresholds that Telemetry responds to and define the autoscaling group.
  • Environment file - Defines the build information for your environment: which flavor and image to use, how to configure the virtual network, and what software to install.