Using templates

Hello all,
I want to start using a template for our existing index. The way we have our process in place is we have various lambdas that process request and they in-turn send their CW logs to a single lambda which send the data to ElasticSearch.

If we start using a template for the existing index, how would we incorporate the lambda so that as part of sending the request to ES it also passes thru what template to use?

When you setup the template you setup the pattern of the indices you want to use it on. If it is an existing index the template will not effect it (Index was created before the template was put in place). You will have to either reindex or delete the index.