Watcher alert for cluster nodes memory and disk

Hello friends,
I want to know how I Can configure a watcher to alert when Elasticsearch nodes free memory or free disk space goes below a threshold?
I mean what input search I should use in watcher JSON?
Can you give me a sample?
Thank you

yes you can use watcher to call elastic APIs. https://www.elastic.co/guide/en/elasticsearch/reference/current/input-http.html

Refer topic "Calling Elasticsearch APIs" where you can know about your full cluster stats such as "OS, Mem, Storage etc". Hope this answers your question.