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Multiple RDS standby instatnces

in the RDS example,  there are two standby Maria DB, is it supported to have multiple standby RDS instances to the other AWS RDS

Saed Alavinia

I actually have the same question as you and I am pretty sure AWS (with the exception of Aurora) doesn’t support multiple Multi-AZ instance. It’s just ONE additional instance.

Saed Alavinia

This make Scott’s slide very confusing. If it is about standard RDS for Mariadb/MySQL, then does it support more-than-one Multi-AZ instance? (I doubt it). If it is Aurora, then it must be specified on the slide.

2 Answers

Hi Bdwidar,

In the example you’re talking about, those other MariaDB RDS databases are Read Replicas which are different than "standby" instances.  You can promote a read replica to the master though.

For a multi-AZ RDS deployment, you do have standby’s that are located in other AZ’s and will automatically assume the Master role if the master fails.  That’s the distinction between read replicas and multi-AZ.


Saed Alavinia

Hello Scott. Unfortunately I have to down vote your answer 😂 since you do not really address the question.

Saed Alavinia

The question here is: "Does AWS Support More-than-one Multi-AZ?" The question is raised because in your slide you are showing more than 1 standby (Multi-AZ) instance, specifically 2 instances in two distinct availability zone.

Saed Alavinia

I don’t think this configuration is support for non-Aurora databases. You are not showing that this is an Aurora database and as such, you will have many confused students 🙂

To the best of my knowledge, and based on the documentation, multiple standby (Multi-AZ) instances ARE NOT support for non-Aurora databases. For Aurora databases, we know that they replicate it across 3 AZ. But if it is not Aurora, you can only have 1 standby database.

See the documentation here:

Which states: 

creates a primary DB Instance and synchronously replicates the data to *a standby instance* in *a different Availability Zone (AZ)*

I’m pretty sure Saed is correct here: a multi-AZ RDS (such as Maria or MySQL) is a 2 AZ "master-slave" configuration. In regions with more than 2 AZs, there is not a replica in each AZ (unless you use read replicas), there is just one DB in each of 2 AZs, one of which is the "active master". In the case of disruptive upgrades, the "standby" DB will be upgraded, the system will fail over to that instance, and the previous master will be upgraded. However, there are just the 2, not one in each AZ.


I think that is the case too. All documentation talks about a standby and in a availability zone (not in plural). In console you are also only asked if you want multi-AZ (yes/no). Created multi-AZ has no options to modify or add new standby instances or at least I found none. Pricing also is consistant: no standby, pay $x with standby pay $x+$x ie for another single server.

Travis C Kirk

+1 to this. As another approach to verify this, if you deploy a Multi-AZ instance and enable log exports to Cloudwatch, you’ll see one log stream per node, and you will only see 2 log streams in this case (at least for MS SQL).

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