CODEWITHSUNDEEP
amazon-ec2scalabilityamazon-rds
Nick
Nick

Reputation: 271

Two Questions Regarding AWS' RDS Multi AZ

  1. I understand that when upgrading to a Multi-AZ rds from a Single-AZ, there occurs a "breef i/o freeze". What exactly does that mean?

  2. When an upgrade is made to a Multi-AZ deployment, say from small to large, will the production database be impacted at all? Will it be able to use the backup databse, then failover?

Upvotes: 15

Views: 8289

Answers (3)

billias
billias

Reputation: 825

Is question 1 still valid? According to AWS documentation (2022) there is no downtime, but there is a small decrease in performance.

Quoting AWS documentation:

When converting a DB instance from Single-AZ to Multi-AZ, Amazon RDS creates a snapshot of the database volumes and restores these to new volumes in a different Availability Zone. Although the newly restored volumes are available almost immediately, they don’t reach their specified performance until the underlying storage blocks are copied from the snapshot.

Therefore, during the conversion from Single-AZ to Multi-AZ, you can experience elevated latency and performance impacts. This impact is a function of volume type, your workload, instance, and volume size, and can be significant and may impact large write-intensive DB instances during peak hour of operations.

Upvotes: 2

Chris Fregly
Chris Fregly

Reputation: 1530

the downtime when converting from single-AZ to multi-AZ is essentially the time it takes for a new instance to launch and become fully functional as sanket said, it may take a few mins.

scaling up a multi-AZ deployment first scales up the slave instance, then performs a failover. the downtime is the time it takes to do the actual failover - usually closer to a minute.

scaling out a multi-AZ deployment is done by adding additional read-replicas (sourced off of the standby) which incurs no interruption. keep in mind that adding read-replicas creates an eventually consistent system which may or may not be desirable.

it's also worth nothing that you should use the same instance types across all multi-AZ instances, otherwise the imbalance may incur replica lag.

as you're probably realizing, it's best to start with a multi-AZ configuration from the beginning. it makes scaling up and scaling out a lot easier and with less downtime.

Upvotes: 7

Sanket Dangi
Sanket Dangi

Reputation: 1195

Answers to your questions are written down :

  1. When you choose to move from Single AZ to Multi AZ, brief I/O freeze happens. It means that for some duration database won't be accessible. No read,write operations will be performed on the database. Mostly, the duration for this is around 3-4 minutes.

  2. Yeah, production database will be affected when you resize the compute(from small to large). The best idea to perform resize operation is during scheduled maintenance window. If select Apply Immediately option, for sometime the database won't be accessible(time to switch control to backup server).

Regards, Sanket Dangi

Upvotes: 10

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