Autoscaling User Guide

Providing autoscaling related parameters

A set of parameters are provided to calibrate the elasticity of the system. This is done in the following manner based on the type of service:

• WSO2 Carbon services
  Define the autoscaling related parameters before WSO2 Elastic Load Balancer (ELB) starts up. (Soon we will support the dynamic behaviour for Carbon servers).

• Non-Carbon services
  Define autoscaling parameters when subscribing to a Cartridge.

Description on autoscaling related parameters

The configuration of the autoscaling related parameters vary based on the type of the service. The autoscaling related parameters for Carbon services are configured using the loadbalancer.conf file, while non-Carbon services are configured at the time of subscription.

• autoscaler_task_interval (t)
  The time period between two iterations of an ‘autoscaling decision making’ task. You are advised to consider the time ‘that a service instance takes to join ELB’ when configuring this value. This is in milliseconds and the default value is 30000ms.
  
  
• max_requests_per_second (Rps)
  The number of requests, a service instance can withstand per a second. It is recommended to calibrate this value for each service instance and if needed for different scenarios. Load testing a similar service instance is an ideal way to estimate the value.The default value is 100.
  
  
• rounds_to_average (r) 
  An autoscaling decision will be made only after this many iterations of ‘autoscaling decision making’ tasks. The default value is 10.
  
  
• alarming_upper_rate (AUR)
  The upper bound of the alarming rate that provides a hint on when to scale up the system. We scale the system up when it reaches the request capacity that corresponds to alarming_upper_rate, without waiting till the service instance reach its maximum request capacity. The alarming_upper_rate is 1. This value should be 0<AUR<=1 and default is 0.7.
  
  
• alarming_lower_rate (ALR)
  This is the lower bound of the alarming rate that provides a hint on when to scale down the system. This value should be 0<ALR<=1 and default is 0.2.
  
  
• scale_down_factor (SDF)
  This factor is needed to make the scaling down process slow. Scaling down needs to be done slowly to reduce scaling down due to a false-positive events. This value should be 0<SDF<=1 and default is 0.25.