How to model a one to many relation in Apache Kudu?

I am trying to model a one-to-many relation in Apache Kudu.

To sum up, Apache Kudu doesn't have:

• foreign keys
• array data types
• JSON support

So the usual ways to model aren't available.

How can I model the relation?

Kudu is not designed to be a relational database. It is just (tabular) data store. The data-processing is done using other frameworks such as Spark or Impala.
It is meant to be used as OLAP system and hence does not enforce any kind relational constraint or transactions. The primary key constraint is needed for Kudu to work (due to the way it is built).

The best way forward would be to extract data from other operational RDBMS and load into kudu if you are already using Spark/Impala for analysis. I would highly discourage using Kudu as a transactional operational database, due to its limitations and Kudu is still very young.
If you need these capabilities consider using traditional RDBMS (postgres/MySql/Oracle/SqlServer etc).