SQL Server Always On Availability Group Zero Downtime Update Procedure

Here I have a 2-node SQL Server 2016 AlwaysOn Availability Group cluster, with 1 primary and 1 secondary.

The question is - what is the optimal way to install Microsoft Updates on the servers in the cluster? I have struggled to find good, clear recommendations on this.

Here is my current thinking:

1. Install updates using Microsoft Update on the secondary
2. Restart the secondary to finish the updates
3. Perform a manual failover from the Primary to the Secondary
4. Install updates using Microsoft Update on the new-secondary (former primary)
5. Restart the new-secondary (former primary)
6. Perform a manual failover from the new-Primary to the Secondary, making the original primary the primary again

My understanding is that this will:

• Cause absolutely no application downtime
• Cause no syncing errors
• Cause no data corruption
• The cluster will not generate errors when half the nodes are updated and the other half are not

Is this correct? Is there a better way to do this?

Thanks in advance - any help is greatly appreciated.

Here's a step-by-step guide on how to achieve what you want:

Apply SQL Server patches or cumulative updates in SQL Server Always On Availability Groups

You might scroll down right to the "Preparatory Phase" section skipping all the "water".