About Index Templates

I have a query regarding index templates. When a template is added does it mandate that all data being written to that index must contain the fields defined in the template? Or does it define how to handle the fields defined in the template if they're present?


The mappings put in place e.g. by an index template mandate how fields are mapped if present. The fields themselves don't become mandatory, and unless you disable dynamic mapping documents may specify fields not present in the predefined mappings.