Difference between revisions of "Heat/Blueprints/ScalableResourceGroup"

Revision as of 16:28, 10 August 2015

< Heat Launchpad Entry: HeatSpec:ScalableResourceGroup
Created: 26 July 2015
Contributors: Ahmed El-Khouly

Summary

Heat Resource Group types provide a convenient way to create several instances of identically configured nested resource maintain the size and readability of heat templates.
Heat provides for two types of resource groups:
(1) OS::Heat::ResourceGroup:

     - Provides the ability to access a single resource attributes with the resource index.

     - Provides an index_var variable that resources use to be replaced with resource index. 

     - Possible change of group size by changing count property and update the parent stack.
 

(2) OS::Heat::AutoScalingGroup/Policy:

     - Dynamic change of group size triggered by signals.

     - Policy defining characteristics of scale operation (size of adjustment, size of adjustment, cool down period).

     - Group changes size by performing nested stack update. 

Some cloud applications need a resource group type with the following features:
- Scale changing group size. This needed to respond to change in workload.
- Added ability of removal or addition of specific resources. This is needed for healing a specific resource by removal followed by addition

 of the same resource (same resource index). It also allows for vnf controlled deloading sequence during scale-in ooperation.

Release Note

TBD

Rationale

Some cloud applications need a new resource group with the following features:
1) Create an initial number of identically configured nested resources.
2) Address single resource within the group using the index with the ability to specify a variable to be replaced by the index.
3) Add(Remove) specific resource within the group by specifying the indices of involved resources.
4) Scale out(in) by adjusting the group size (with a certain increment) when user defined triggers are met.

User Stories

1) Recreate a (failed) resource by adding/deleting the corresponding nested resource in the group.
2) Add new resources to group when certain criteria met(ex. increase in workload).
3) Remove a number of resources according to a predefined criteria(increasing or decreasing order of age or index).
4) Specify certain resources for removal.

Assumptions

None.

Design

(1) Define a new heat resource type: OS::HEAT::ScalableResourceGroup with the following properties:

   resource_def : Map
    Resource definition for the resources in the group. 
    Required property.
    Can be updated without replacement.

   index_var : String
    A variable that this resource will use to replace with the current index of a given resource in the group. 
    Updates cause replacement.
    Optional property, defaults to “%index%”.

   initial_size: Integer
    Initial number of resources in the group at creation time.
    Optional property, defaults to 1.
    The value must be at least 0.

   max_size: Integer
    Maximum number of resources in the group.
    Optional Property, defaults to 1.
    Updates can cause creation/deletion of some resources according to scale_in_criteria/scale_in_order.
    The value must be at least 0.

   min_size: Integer
    Minimum number of resources in the group.
    Optional property, defaults to 1.
    Updates can cause addition/removal of resources according to scale_in_criteria/scale_in_order.
    The value must be at least 0, less than or equal to max_size.

  scale_in_criteria:String
   Removal criteria of resources in the group.
   Optional property, defaults to "Index".
   Possible Values: "Index" or "Age"

  scale_in_order:String
   Removal order of resources in the group according to the specified criteria.
   Optional property, defaults to "Decreasing". 
   Possible Values: "Increasing" or "Decreasing"

  scale_batch_size:Integer
   Number of resources to be added/removed simultaneously.
   Optional property, defaults to 1. 
   Possible Values: "Increasing" or "Decreasing"

  scale_batch_pause:Integer
   Number of seconds between batches.
   Optional property, defaults to 0. 

(2) Introduce ScalableResourceGroup class inherits from ResourceGroup. The new class adds a signal handler for signals with the following specification:

     command: String
      Actions to perform on the group.
      Possible Values: "ADD", "REMOVE", RECREATE, "SCALE_OUT", "SCALE_OUT" 

     parameters: depends on the command
      - ADD/REMOVE/RECREATE parameters:
         resources: List of Integers
          list of resource indices to add, remove or recreate
    
      - SCALE_OUT/SCALE_IN parameters:
         scale_size: Integer
          Size adjustment. 
          Value Must be positive.