Introductory is this:
There are two applications with their own databases (one web, a second enterprise server application). Both applications different databases. Both applications have API. When adding information to a web application (for example, you can take new user registration) - the data must first send to the database server, and after (or in parallel) in the database of an enterprise application (using API of course). If any data is added to the enterprise application, they are respectively at the beginning are stored in database and then sent get request to store the data in the database of the web application.
The question is how to most effectively implement on the server (using the Apollo server Node) the first part where the data changes on the site and therefore need to keep both bases . Just specify that the implementation must use the API as a database-level fail to realize synchronization. Knowledge of JS is very small, so primarily looking for examples or a detailed article with the realization of such.