Add convenience functionality around exposing NiFi listener ports with kubernetes services

[soenkeliebau]

Follow up ticket to #317

Processors in NiFi can expose ports and listen for connections on these.

For clients to access these endpoints, the nifi-operator has to expose the http(s?) ports prior to creating the workflow (i.e. at cluster creation time).

Investigate a proper way to implement this.

Questions

• How to support multiple rest triggered workflows (multiple ports)?
• How to provision SSL certs per workflow?
• In a distributed Nifi cluster, should http(s) endpoints be published from all (nifi) pods?
• ...

09.08.2022 meeting minutes

We see two possible solutions. The first one involves configuring a proxy to all Nifi cluster nodes. The second and preferred solution involves polling the Nifi api for listeners marked with a stackable attribute and patch a k8s load balancer service accordingly.