This can be 2 parts,
1. Feature upgrades, version upgrades of infra services - We will plan for this without any downtime, by splitting it into multiple segments or having a backup during that period. If any restart is required, there could be a downtime of certain components during the restart. But we will inform about this well in advance to our customers.
2. For AWS recommended patch updates - This would have downtime, but will be for a very short period, affecting only a few components.