- Will old backups not work anymore?
Yes, you can still restore from a 3.4 backup. You will need to restore a 3.4 backup to a 3.4 cluster then upgrade that cluster to version 3.6.
- How long does the upgrade take?
There is no fixed length of time because it will depend on factors such as the number of nodes that need to be upgraded.
- Will the cluster be offline during upgrade?
Atlas always upgrades the cluster using a rolling process to maintain cluster availability.
Please let me know if you have questions on any of the above.