andrewmlim commented on issue #3725: NIFI-6558 Added Parameters to User Guide and Sys Admin Guide URL: https://github.com/apache/nifi/pull/3725#issuecomment-531266412 > * Variable values cannot reference other variables or make use of Expression Language. > Thanks for updating the docs @andrewmlim! I pointed out a handful of notes that I think could be clarified slightly. It may also make sense to point out a few additional notes: > > * Parameters cannot be referenced in Reporting Tasks currently, or in Controller-Level Controller Services. > * While most processor/controller service properties are not validated when referencing variables / using Expression Language, they will be validated (against the substituted value) when using Parameters. This is a nice advantage of Parameters over variables. > * Variable values cannot reference other variables or make use of Expression Language. > * It may be worth explaining how variables work when interacting with the Flow Registry. When exporting a flow to the flow registry, the name of the parameter context is sent for each process group that is stored. Additionally, the parameters (names, descriptions, values, whether or not sensitive) are stored with the flow (for sensitive params, the values are not stored). When a flow is imported / updated, if no parameter context is already set, NiFi will set the Parameter Context with the same name as the one stored in flow registry. If none exists with that name, it will create one. It will also add in values for any missing parameters, based on the values that were exported to the flow registry. Even though sensitive values are not stored in the flow registry, this is a huge improvement over variables, because of Parameters are used, it's very easy for the user, on import/upgrade, to just go in and define the values for the Parameters, including sensitive values. If using Variables, users had to search for sensitive properties to fill in the values, etc. And since all properties in the flow can now be parameterized, it is now easy, when designing the flow, to parameterize things that will change per-deployment, and then have just one place to fill in all of these values when importing the flow. Thanks for the comments @markap14 ! I'll edit my PR with these Notes. For the last bullet re: Flow Registry integration, I agree we need to cover this topic in more depth, however I was planning on doing that in a separate Jira/PR.
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