This project is an example of how to implement rate limit in different databases.

In this project I am using:
Spring boot application. Mysql server. H2 database to represent elastic search database. Maven

To cover this rule:

During the day 9:00 - 17:00 (UTC) we use MySql as a source
During the night 17:01 - 8:59 we use Elastic
I implemented AbstractRoutingDataSource pattern from spring boot.

This project includes both unit tests and integration tests.

just execute it using maven or ide. obs: make sure to have mysql instance running.

The API documentation is generated using OpenAPI 3.0 and can be accessed at http://localhost:8080/swagger-ui.html and http://localhost:8080/v3/api-docs.

In order to see and interact with your db, access the h2 console in your browser. After running the application, go to:

http://localhost:8080/h2-console

Enter the information for the url, username, and password in the application.properties:

url: jdbc:h2:mem:test
username: sa 
password: password

this project doesn't sync databases.

Possibles approachs to do it:
Create a scheduler to run based on cron job to sync all databases.
Create a event first approach to insert on all intances.
Use a middleware to sync databases.