We have not talked to teams who implemented Great Expectations on NiFi yet, so there is no published how-to guide for this integration.
Here are a couple of pointers that should help:
Since NiFi allows running arbitrary Python code, integrating a validation step into a NiFi pipeline should look very similar to doing this in Airflow.
We have an example repo that shows an Airflow pipeline with Great Expectations integrated here: https://github.com/superconductive/ge_tutorials/tree/main/ge_dbt_airflow_tutorial
See this section where we define a node in the Airflow DAG that validates the input data using Airflow’s PythonOperator: https://github.com/superconductive/ge_tutorials/blob/main/ge_dbt_airflow_tutorial/airflow/ge_tutorials_dag_with_great_expectations.py#L185
Please publish anything that will be helpful to the community. If you need further help with this, ping us in our Slack: https://greatexpectations.io/slack
If more users are interested in this integration, please “thumb-up” this GitHub issue: https://github.com/great-expectations/great_expectations/issues/1891