Hi Imesh, Lakmal, Devs, Following the attached email thread, this email is intended as a starting point in formalising the proposal of the proceeding autoscale enhancement.
Kind regards, Mike… Proposal for ‘Transition Compensated Continuous Scaling’ enhancement to be added to Apache Stratos Autoscale feature to: 1. 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) 2. 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. From: Michael Hall <micha...@cisco.com<mailto:micha...@cisco.com>> Reply-To: "dev@stratos.apache.org<mailto:dev@stratos.apache.org>" <dev@stratos.apache.org<mailto:dev@stratos.apache.org>> Date: Friday, 13 February 2015 11:36 To: Lakmal Warusawithana <lak...@wso2.com<mailto:lak...@wso2.com>>, "dev@stratos.apache.org<mailto:dev@stratos.apache.org>" <dev@stratos.apache.org<mailto:dev@stratos.apache.org>>, Imesh Gunaratne <im...@wso2.com<mailto:im...@wso2.com>> Subject: Re: autoscale architecture That’s a good plan, My work number is +442088242650 I’m around now, but will break for a while for lunch in an hour or so. Cheers From: Lakmal Warusawithana <lak...@wso2.com<mailto:lak...@wso2.com>> Date: Friday, 13 February 2015 11:24 To: "dev@stratos.apache.org<mailto:dev@stratos.apache.org>" <dev@stratos.apache.org<mailto:dev@stratos.apache.org>>, Imesh Gunaratne <im...@wso2.com<mailto:im...@wso2.com>>, Michael Hall <micha...@cisco.com<mailto:micha...@cisco.com>> Subject: Re: autoscale architecture Shall we go for a call, it will be more productive. On Fri, Feb 13, 2015 at 4:45 PM, Lakmal Warusawithana <lak...@wso2.com<mailto:lak...@wso2.com>> wrote: Hi Michael On Fri, Feb 13, 2015 at 4:14 PM, Michael Hall (michaha2) <micha...@cisco.com<mailto:micha...@cisco.com>> wrote: Hi Imesh, So ‘transistion compensated’ refers to cartridges, which are ’transistioning’ between SPAWNED-ACTIVE, and TERMINATING-TERMINATED. What it really means, is that if the 'aggregated average’ (Referred to this as <metric>PredictedValue in scaling.drl) is compensated: 1. As if the ‘spawning’ cartridges are providing resouce (although they aren’t yet) 2. As if the ‘terminating’ cartridges have removed resource (although they haven't yet) Such that the ‘transition compensated aggregated average', will be approximately what the actually aggregated average would be if those cartridges had become fully ‘active’ or ‘terminated’. This means the ‘transition compensated aggregated average’ is always in a sensible state to make a scaling decision. This then allows us to make a scaling decision as often as we’d like (much smaller than 90 seconds, could even be every 1 second), because if you take the example the we’ve scaled up, the 'transition compensated aggregated average’ will instantly adjust to N/N+1 of it’s raw value (copied formula from previous email for reference below), so another scaling decision will only occur, if the underlying load (aggregated average) increases even further. transistion-compensated-agg-ave = agg-ave * ( cluster-size / cluster-size + cluster-spawned-size - cluster–terminating-size ) I think this is good proposal, definitely it will help to calculate more accurate agg-ave values. Since CEP has the topology information we can easily calculate this. AFAIK, auto scaler take care of cartridge states when calculating required instances count for a predicted load. I’d be more than happy to setup a webex meeting to try and explain this better? Or another avenue of communication at your preference? Kind regards, Mike From: Imesh Gunaratne <im...@apache.org<mailto:im...@apache.org>> Reply-To: "dev@stratos.apache.org<mailto:dev@stratos.apache.org>" <dev@stratos.apache.org<mailto:dev@stratos.apache.org>> Date: Friday, 13 February 2015 01:09 To: dev <dev@stratos.apache.org<mailto:dev@stratos.apache.org>> Subject: Re: autoscale architecture Hi Mike, Thanks for the detailed explanation of your question. Currently we do not have the capability to do this in runtime for a specific cartridge. However we could reduce the global scaling decision interval. This needs to be configured at three locations: 1. Cartridge agent statistics publishing interval (default: 15 seconds) 2. CEP execution plan/faulty member detection interval (default: 1 min) 3. Autoscaler cluster monitor interval (default: 90 seconds) I did not clearly get what you mean by 'transition compensated'. Is there a way to explain it further? Thanks On Fri, Feb 13, 2015 at 12:26 AM, Michael Hall (michaha2) <micha...@cisco.com<mailto:micha...@cisco.com>> wrote: Hi Dev, Thanks for your response Imesh, if its ok, I’d like to skip straight to my (rather lengthy) question: Does the autoscaler have, currently or plans to introduce, a means to receive an asynchronous event, signalling that a cartridge has gone from ‘SPAWNED’ to ‘ACTIVE’, after it is launched from a 'scale-up’ decision, so that, scaling decision interval can decrease to approximately the metric update interval, and multiple cartridges are not spawned when only one is needed? In more depth: The reasons for my question being that by knowing a cartridge is in the ‘SPAWNED’ or ’TERMINATING’ state, the aggregated metric averages can be ’transition compensated’ I.e… transistion-compensated-agg-ave = agg-ave * ( cluster-size / cluster-size + cluster-spawned-size - cluster–terminating-size ) To allow the scaling decisions to occur on a continuous (only throttled by the metric update frequency) basis. It appears that currently scaling decision occurs ~minutes. If this becomes ~seconds, it would vastly improving the maximum rate of ascent a cluster can scale against sudden increase in load. It appears that there is no spawning state awareness, which also means several ‘redundant’ instances get spawned, when instance startup time is greater than the scale decision interval. Finally: Are there difficulties in tracking ‘SPAWNED’ to ‘ACTIVE’ state on a per cartridge basis, how does this align (if its a valid enhancement) with other potential improvements that could be made to the autoscaler? Regards, Mike From: Imesh Gunaratne <im...@apache.org<mailto:im...@apache.org>> Reply-To: "dev@stratos.apache.org<mailto:dev@stratos.apache.org>" <dev@stratos.apache.org<mailto:dev@stratos.apache.org>> Date: Thursday, 12 February 2015 18:16 To: dev <dev@stratos.apache.org<mailto:dev@stratos.apache.org>> Subject: Re: autoscale architecture Hi Michael, Yes you can ask any questions you have on Autoscaling here. I don't think we have documented Autoscaling feature in 4.1.0 at the moment. However you could find some information here [1]. Autoscaling has slightly changed with Composite Application Model. [1] https://cwiki.apache.org/confluence/display/STRATOS/4.1.0+Autoscaler Thanks On Thu, Feb 12, 2015 at 9:33 PM, Michael Hall (michaha2) <micha...@cisco.com<mailto:micha...@cisco.com>> wrote: Hi Devs, Is there a resource or contact that can help me understand the current, and planned architecture of the autoscaling feature within Stratos. Best Regards, Mike -- Imesh Gunaratne Technical Lead, WSO2 Committer & PMC Member, Apache Stratos -- Imesh Gunaratne Technical Lead, WSO2 Committer & PMC Member, Apache Stratos -- Lakmal Warusawithana Vice President, Apache Stratos Director - Cloud Architecture; WSO2 Inc. Mobile : +94714289692<tel:%2B94714289692> Blog : http://lakmalsview.blogspot.com/ -- Lakmal Warusawithana Vice President, Apache Stratos Director - Cloud Architecture; WSO2 Inc. Mobile : +94714289692 Blog : http://lakmalsview.blogspot.com/
