After rolling over, new index doesn't have dynamic template mappings from old one

In elasticsearch 6.4, I have an alias /foo which had an index of the format /foo-000001. This index was created with a mapping which also included dynamic template. When data grew, I rolled over using

POST /foo/_rollover
  "conditions": {
    "max_age":   "30d",
    "max_size": "500gb"

Rollover worked as expected and resulted in the creation of foo-000002, but to my surprise and disappointment I lost the mappings created via dynamic templates. Any idea where it went wrong or what I may have missed during rollover?

You need to include the mapping and setting in your rollover call.
It's not automatic unless you use template.

thanks, it makes sense now