How could I connect to external database safely?

Currently we are planning to host our api service on Railway. But we do have external data which need to connect to e.g. kafka, and MSSQL. How can we have private connectivity to our in house database?

add the connection details to service variables, and use those environment variables in code

It might have vulnerability. The connection expose to public, i can't convince to my investor to using Railway as a design of this, i am thinking to use 2 way ssl connection.

okay then tailscale private network

is tailscale a vpn? how is it work to your Railway platform?

it would be something you would need to add to your app yourself, you can do some research if you are unsure of what it is

noted. Thanks @Brody