This blog will talk about a scenario where you have multiple Virtual Private Clouds (hereafter referred to as VPC), and you need to access a private app hosted in one VPC from another VPC. An example of this scenario could be that you have a VPC for your staging environment and another VPC for production environment, then you'd like to sync the database from of production environment from the staging environment. In this case, it might not be straight forward to do this, as you might not be able to access the production database from outside the production VPC.
One of the solutions for this problem would be to first take a dump of the production database on one of the public facing machines in the production VPC, and then copy that dump to a public facing machine in the Staging VPC and finally applying this dump to the private database of Staging environment. This approach will work, but it would not be a perfect solution, as you have to copy the db dump between VPC's.
A much better approach would be if you could directly connect to the production database from the Staging VPC & execute the dump & restore command, for that you need direct access of production database from staging environment. This approach is called port-forwarding. We configure port-forwarding at one of the public facing machines(NAT is the preferred one) in the production VPC in such a manner that if a request comes on this machine at port x it will be forwarded to port y on a private facing machine in the production VPC which is the database production in this case.
In the next blog I will talk about other alternate approaches that can be used to solve this problem.