ETL Between MySQL Primary Datastore and MongoDB Secondary Datastore

We have a rails application with a MySQL backend, each client has one DB and the schema is identical. We use a custom gem to modify the DB based on the request url (this is some kind of legacy code we're trying to move away from)

We need to commit some changes from these MySQL databases (inventory changes, order information, etc.) and store them in one MongoDB database (multi-trend datastore), this data will be used for analytics first, but ours The idea is to move everything.

There was something that could be done using AR and rabbit callbacks, but honestly it was wrong and it looked like it was harder to fix it than starting a new approach.

We did some research and found some ETL tools, but they exceeded our needs.

Does anyone have any experience with a similar problem?

Guidelines for Building and Implementing This Simple ETL