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https://issues.apache.org/jira/browse/NIFI-4994?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16406654#comment-16406654
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Sivaprasanna Sethuraman commented on NIFI-4994:
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I could be wrong but NIFI-4864 covered a part of what you have mentioned here
(reloading additional classpath resources on component restart). I assume this
is more of code related restart (static objects) but just wanted to highlight
that.
> Reload instance class loader at every component restart
> -------------------------------------------------------
>
> Key: NIFI-4994
> URL: https://issues.apache.org/jira/browse/NIFI-4994
> Project: Apache NiFi
> Issue Type: Improvement
> Components: Core Framework
> Reporter: Koji Kawamura
> Assignee: Koji Kawamura
> Priority: Major
>
> h2. Current Class loader reload mechanism
> NiFi framework provides RequiresInstanceClassLoading to annotate components
> (Processor, Controller Service or Reporting Task) to use per instance class
> loader. Instance class loaders are reloaded when associated components are
> restarted, if any component property flagged as
> 'dynamicallyModifiesClasspath' is updated. Such component property is used to
> let user specify additional class pass resource URLs. E.g. PutHDFS
> 'Additional Classpath Resources'.
> h2. Limitation of current mechanism
> Current mechanism requires component properties to trigger reloading to
> represent class path resource URLs. That works well in scenarios for users to
> add/del/mod additional class path resources.
> However there is different needs for reloading instance class loader. That is
> re-initializing static state in dependencies.
> For example, ReportLineageToAtlas reporting task uses Atlas client library,
> and the library has static code blocks to initialize its dependencies, such
> as Kafka client with parameters passed by NiFi reporting task based on user
> inputs. Once the initialization is done, there is no way to re-initialize
> those objects, meaning even if NiFi user changes reporting task
> configuration, those will not be able to reflected.
> https://github.com/apache/atlas/blob/master/notification/src/main/java/org/apache/atlas/hook/AtlasHook.java#L63
> The only possible operations to reset such static state are, creating another
> instance, configure the instance again, remove the old one and start new one.
> Or restart NiFi process. This limitation affects UX negatively.
> h2. Improvement design
> Possible approaches are:
> # Enhance RequiresInstanceClassLoading annotation so that custom components
> can specify whether it needs to be reloaded on every component restart
> without condition.
> # Add new PropertyDescriptor instance field to denote that instance class
> loader needs to be reloaded if a property is changed. Similar to
> 'dynamicallyModifiesClasspath' but for configurations other than URI. Then,
> include those property value to
> AbstractConfiguredComponent.additionalResourcesFingerprint
> No.1 is more naive approach, but require less framework code change. No.2
> looks redundant, also could be error-prone, e.g. by forgetting to mark some
> properties.
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