How to upgrade from v3.6.3 to v4.4.5?

Ops and Admin Installation & Upgrades
4

There is probably a reason why the docs says it’s not compatible. If you can afford to be offline, then in your situation I would:

  • Take one of the node and stop it.
  • Take a copy of the data folder (/db/data by default) and move it to another server.
  • Upgrade it to 4.0 following the 4.0 upgrade doc.
  • Restart the node in 4.0 standalone.
  • mongodump the 4.0 node.
  • create the new 5.0 or 6.0 (soon!) 3 nodes cluster.
  • mongorestore in this new cluster.

I think this would be safe. And in case something goes wrong, you still have your 3.6 nodes completely untouched and safe.

Cheers,
Maxime.