Is it possible to specify a partition key when using filebeat to send to a Kafka topic?

Elastic Stack Beats
5

I am not sure how to get the id. here is my setup:

- input_type: log
  paths:
    - /logs/myservice.log
  include_lines: ["End request ip:(?P<ipaddress>[^,]*),"]
output.kafka:
  key: '%{[ipaddress]}'

and my log line is like
2017-07-31 11:51:51,766 INFO - End request ip:32.40.65.43,......
I can get the log line in kafka, but the key is still empty.
Is it possible at all?
thanks.