Major Upgrade version- 0.49 to 3.0.4

We have been working on our Rocket chat deployment inside offline network environment in the past 3 years.
We started with version 0.49, we sticked to it without upgrading due to custom changes we made.

Now that we are ready, we intend to upgrade to version 3.0 or higher.
What are the steps needed for the upgrade to succeed? with migrations of our data (i.e: files, db, etc…)

Since we’ve made some modifications to the db models and source code, I assume we’d need some way of making our version compatible with the migrations that Rocket Chat has. If that’s the case, how do we add a custom migration to make our version compatible to undergo the official migrations up to version 3.x

Thanks for your help :slight_smile:

  • Version of Rocket.Chat Server: 0.49
  • Operating System: linux (ubuntu 18.04)
  • Deployment Method: tar build from bundle
  • Number of Running Instances: 21
  • NodeJS Version: 4.5
  • MongoDB Version: 4.0, replica set

Any help or ideas???