Please note that I'm only using one node of ElasticSearch (not a cluster of nodes).
Look, I found this on the website:
TIP: In order to reduce the number of indices and avoid large and sprawling mappings, consider storing data with similar structure in the same index rather than splitting into separate indices based on where the data comes from. It is important to find a good balance between the number of indices and the mapping size for each individual index.
So, probably it's better to have a single index. Is that correct?
That way, I'll save the client as a property of the post.