I have a question regarding the concept of parameter context.
The admin guide says : A Process Group can only be assigned one Parameter Context, while a given Parameter Context can be assigned to multiple Process Groups.
OK, let's assume you have internal kafka or database, and some external system you connect to. You might want to have a parameter "group"
for the internal kafka connection, and another parameter contexts for each external system connection.
However, your flow, clearly a part a process group, reads data from external system and stores data internally. Thus you need actually 2 connections in the flow,
it means 2 parameter contexts, which is not possible. To solve that, you assign the connections (controller services) to the parent group and the parameters.
Finally, for connections which are common to many flows, like your kafka, databases, and HttpSSL you land in the parent NiFi Flow, having parameter context which contains
a bunch of pretty unrelated parameters (for kafka, databases, ..).
What is see, there is hardly a possibility to reuse parameter context
as they cannot be combined and thus you have 1:1 relationship between par. context and group just like for variables assigned to a processor group.
Did I miss something? What is actually the big advantage of parameters over variables?
Variables are deprecated. Parameters are new and easy to externalize. I can use them in devops processes via REST, NiFi CLI and Python. You can programatically build parameter contexts and parameters and assign them to process groups.
Parameters are getting some upgrades to do some of the more advanced things you mentioned.
And they help power stateless nifi.,
NiFi Variables can only be used by component properties that support NiFi's Expression Language (EL).
NiFI Parameters can be used in ANY component property including those that are encrypted. This gives more flexility to users, especially those users who use NiFi-Registry to promote version controlled Process groups across multiple NiFi instances/clusters. It is often the case that different environments have different URLs and passwords in use within the same dataflows. A Dataflwo can thus be promoted to another environment that simply uses different Parameter values thus not requiring the user to update a large number of components each time a new version of flow is promoted from one environment to another.
You are correct that Parameters are similar to Variables in respect to assignment to a process group. You can only have one Parameter context assign to a Process Group.
Hope this helps,