The use case I got was to connect to a 2nd Db, to retrieve data from a 2nd database and respond with a JSON string, the request would come in as an API call that looks like this “localhost/api/1/noonreport?API-KEY=oBThDgLsHOi8WJpwgf6IvJVQQ45E9LTudUN9i1RL”
I’m using CodeIgniter in the backend server, with MVC and RESTful API support.
The first thing I did was to change the file database.php to add an additional database group to the configuration, like this

As you can see I added a 2nd database group and called it noon, the default group will be loaded automatically during $this->db call.
Then I created a new API function for noonreport as shown here

As you can see I connected to the 2nd database, I fetch the data I needed from the 2nd database – closed the 2nd database connection and created a JSON response, that is all.
If you need help or would like to ask a question, please comment.
1 comments On Connecting backend CodeIgniter to two databases after receiving an API call
Great tip. However, it should also be explained that developers should make it a practice to make sure to close the database connection manually once the code doesn’t require the connection anymore. source: https://www.cloudways.com/blog/connect-multiple-databases-codeigniter/