Michael Hall created STRATOS-1217:
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Summary: Transition Compensated Continuous Scaling
Key: STRATOS-1217
URL: https://issues.apache.org/jira/browse/STRATOS-1217
Project: Stratos
Issue Type: Improvement
Components: Autoscaler
Affects Versions: FUTURE
Reporter: Michael Hall
Benefits:
Greatly improve (~ x100) the maximum rate of cluster size increase (maximum
rate of ascent), when subjected to a sudden increase in load. (continuous
scaling decisions can occur as the decision isn’t delayed (cluster monitor
interval) to wait for the system to tend toward a steady state)
Eliminate redundant cartridges being spawned/terminated because of cartridge
startup/stop being larger than a scaling decision interval (cluster monitor
interval)
Implementation Overview:
- Current:
Measured health statistic -> sent to CEP -> 1 minute average -> forward
prediction (use ave + ave grad + ave 2nd grad) -> use autoscale policy to calc
number of required cartridges -> compare required cartridge count, to current
cartridge found and scale appropriately
- Proposed:
Measured health statistic -> sent to CEP -> 1 minute‘moving’average (per
second) -> forward prediction (use ave + ave grad + ave 2nd grad) -> use
autoscale policy to calc number of required cartridges -> compare required
cartridge count, to ( the active (current) cartridge count + the spawning
cartridge count – the terminating cartridge count ) and scale appropriately
Implementation of ‘spawning’/‘terminating’ cartridge count:
Currently the autoscale feature is not aware of the amount of cartridges in the
cluster that are transitioning to and from the ACTIVE state. The proposed
enhancement relies on being able to know this count at any given moment in time.
This can be implemented by using asynchronous events, where -
‘MEMBER SPAWNED EVENT’ -> increments cluster-cartridge-count-spawned
‘MEMBER ACTIVE EVENT’ -> decrements cluster-cartridge-count-spawned, and
increments cluster-cartridge-count-active
‘MEMBER TERMINATING EVENT’ -> increments cluster-cartridge-count-terminating
‘MEMBER TERMINATED EVENT’ -> decrements cluster-cartridge-count-terminating,
and decrements cluster-cartridge-count-active
Summary:
By compensating the ‘current’ cartridge count/ cluster size, with the
cartridges that are transitioning, we remove the issue of duplicating scaling
decisions whilst also allowing the scaling decision to occur continuously,
greatly improving our ‘maximum rate of ascent’ when scaling up our cluster in
reaction to a sudden increase in load.
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