How to index dump of html files to elasticsearch?

I'd look at the bulk api that allows you to send more than document in a single request, in order to speed up your indexing process. You can send batch of 10, 20 or more documents, depending on how big they are.

Depending on what you want to index you might need to parse the html, unless you want to index the whole html as a single field (you might want to use the html strip char filter in that case to strip out the html tags from the indexed text).

After indexing I'd suggest to make sure the mapping is correct and you can find what you're looking for. You can always reindex using the _source special field that elasticsearch stores under the hood, but if you already wrote your indexer code you might want to use it again to reindex when needed (of course with the same html documents). In practice, you never index your data once... so be careful :) even though elasticsearch always helps you out with the _source field), it's just a matter of querying the existing index and reindex all its documents on another index.