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From "Robert Nettleton (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (AMBARI-15417) Blueprint should have a flag to allow configuring use of RCO vs Retry method
Date Wed, 16 Mar 2016 14:52:33 GMT

    [ https://issues.apache.org/jira/browse/AMBARI-15417?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15197435#comment-15197435
] 

Robert Nettleton commented on AMBARI-15417:
-------------------------------------------

[~bhuvnesh2703], Its not clear if there is an easy path towards enabling the flag that is
described in this JIRA.

I was not the architect behind this implementation change in Blueprints, but the change in
Ambari 2.1.0 was quite extensive, and there is no clear way to provide the older behavior.
 

This means that supporting Role Command Ordering (to simulate the Ambari Blueprints behavior
prior to Ambari 2.1.0  in Blueprints could require a major refactoring that would be quite
a large task. 

The dynamic provisioning model in Blueprints introduced in Ambari 2.1.0 does introduce many
performance and scaling benefits.  Starting a large cluster is now much more fault-tolerant,
since a given node failure will not cause the entire cluster deployment to fail.  This turns
out to be quite important when clusters are large.  

I would propose that a lightweight orchestrator be introduced into Ambari Blueprints, that
would support some level of configurable dependency ordering without sacrificing the gains
achieved in Ambari 2.1.0 that are listed above.  Unfortunately, that is probably not a small
amount of work, but could possibly provide a reasonable balance between the ordering guarantees
of the older model and the performance gains of the model introduced in 2.1.0.  

CC [~sumitmohanty], [~mahadev], [~jspeidel]







> Blueprint should have a flag to allow configuring use of RCO vs Retry method
> ----------------------------------------------------------------------------
>
>                 Key: AMBARI-15417
>                 URL: https://issues.apache.org/jira/browse/AMBARI-15417
>             Project: Ambari
>          Issue Type: Bug
>          Components: blueprints
>    Affects Versions: trunk
>            Reporter: bhuvnesh chaudhary
>
> With Blueprint deploy's, role command oder (RCO) is not honored.
> Currently, in order to mitigate failure for a service start due to dependencies on other
services, blueprint deploy uses retry mechanism to ensure that the services are started and
their prerequisite are met.
> However, retry mechanism in some cases can cause the install / start time to take long
and might need additional logic on component specific installation to handle retries.
> In order to provide with flexibility, we should put up a flag in blueprints which drive
the required behavior. (Use RCO vs Use Retry)
> Say: The flag name is use_rco (Change what seems better))
> By default, the value of use_rco can be false and if someone wan't to override it they
can specify it as true in the blueprint.
> Note: Keeping it as false by default as it has been already there since Ambari 2.1.0.
Hopefully, even if we set this to true by default, it should not impact customers except a
few. But we can make this decision based on communities opinion.



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