I got a really strange behavior on one of our Elasticsearch instances running 6.x regarding the 'mapper cannot be changed' error.
We are using strict mapping on template level and we usually don't have data type changes for the fields. But somehow it has happened, that for some fields the mapping has changed. So now, we have this weird problem that we cannot change the mapping at all or even extend the existing mapping by more fields.
This is the first error message:
"type":"illegal_argument_exception","reason":"mapper [field_amount] cannot be changed from type [float] to [integer]"
Seems fine. Ok, let's change the type back to float:
"type":"illegal_argument_exception","reason":"mapper [field_amount] cannot be changed from type [integer] to [float]"
This is bad. How can I solve this problem, so that I'll be able to change the mapping of the template to add more fields?