MySql Blue/Green deployment 5.7.44 to 8.0.36 fails on DB subnet group doesn't meet Availability Zone coverage.

Could it be because not all of the replicas are in us-east-b with the Master?

This table shows the Availability Zones for each instance in both the blue and green deployments. The Master instance and two slaves (Slave 1 and Slave 2) are set up in both deployments, while Slave 3 and Slave 4 are only present in the blue deployment and not yet created in the green deployment.

Yes, that could be a contributing factor to the error you're encountering. The error suggests that your DB subnet group is not adequately covering multiple Availability Zones (AZs). Based on the table, it seems that the green deployment might be lacking instances in multiple AZs, as both the green Master and green Slave 1 and Slave 2 are in the same AZ (us-east-1c), and there are no green instances in us-east-1b.

To resolve this issue, you should ensure that your DB subnet group for the green deployment includes subnets in at least two different AZs. You may need to create additional green replicas in us-east-1b or adjust your subnet group configuration to include subnets from both us-east-1b and us-east-1c. This will help you meet the AZ coverage requirement for a successful blue/green deployment.

To meet the AZ coverage requirement for both the blue and green deployments, you could adjust your setup like this:

In this adjusted setup:

• Both the blue and green Masters are in different AZs, which is good.
• For the slaves, we've ensured that both blue and green deployments have slaves in both AZs. For example, Slave 1 and Slave 2 in the green deployment are moved to us-east-1b, while Slave 3 and Slave 4 in the green deployment are created in us-east-1c.