Vincenzo Lombardo created NIFI-16502:
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Summary: Restore previous state of referencing components when
re-enabling a Controller Service
Key: NIFI-16502
URL: https://issues.apache.org/jira/browse/NIFI-16502
Project: Apache NiFi
Issue Type: Improvement
Components: Core UI
Reporter: Vincenzo Lombardo
h3. Proposal
Keep a snapshot of the referencing component states in the UI when a Controller
Service is disabled, and offer an additional enable scope that restores it.
* *Snapshot*: when the disable request is submitted, the dialog already has the
full referencing component tree with the current state of each component. The
UI stores the identifier, reference type and state of each referencing
component in browser storage, keyed by the Controller Service identifier, using
the existing StorageService with an expiration.
* *Enable scope*: when a snapshot exists for the Controller Service, the Enable
dialog offers a new scope such as _Service and previously active components_,
showing when the snapshot was taken. Without a snapshot the dialog is unchanged.
* *Restore*: the {{PUT /controller-services/\{id\}/references}} endpoint always
updates all referencing components, so the restore uses the existing
per-component endpoints instead:
** referencing Controller Services that were ENABLED are enabled with {{PUT
/controller-services/\{id\}/run-status}}, waiting for each level to be enabled
before the services that depend on it;
** referencing Processors and Reporting Tasks that were RUNNING are started
with {{PUT /processors/\{id\}/run-status}} and {{PUT
/reporting-tasks/\{id\}/run-status}}.
* Components removed since the snapshot are skipped, and components added since
the snapshot are left unchanged. The snapshot is removed once the restore
completes, and the dialog reports which components could not be started.
This requires no framework or REST API changes and keeps the current behavior
when no snapshot is available.
h3. Limitations
* The snapshot only exists in the browser where the service was disabled. A
service disabled by another user, from another browser or through the REST API
has no snapshot, so the new scope is not offered.
* Restoring N components takes N requests instead of a single request to the
references endpoint.
h3. Alternative
A server-side option would be to let the references endpoint update only a
given set of components, reusing the {{candidates}} support that
{{StandardControllerServiceProvider.scheduleReferencingComponents()}} already
has (introduced for NIFI-6748). The UI snapshot would then only choose the
candidates, and the restore would remain a single request. Feedback on the
preferred approach is welcome before implementation.
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