title: How to make a field indexed in Kibana?
body: <p>I have imported json data from Kafka to elasticsearch and I can see them in Kibana > Discover. But, on the left panel, under 'Available Fields', all my fields have a '?' and says 'Not indexed'. Because of this, I am unable to visualize the data. I read somewhere that I would have to change mapping to make the fields indexed. I couldn't see an example anywhere? Any idea on how I can make my data visualize in Kibana? Thanks.</p>