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Looking at the prices for RDS instances, the multi-AZ instances cost double. Having a production environment in mind, does it worth it?

What uptime should I expect from a single-AZ instance, as opposed to a multi-AZ one? Has anyone had experience running a production DB on both single and multi availability zones?

thefroatgt
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UriP
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1 Answers1

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We have a multi-AZ production deployment with AWS RDS and it's been working fabulously well for the last 3 years.

The multi-AZ catalog page clearly lists out the benefit of using a multi-az vs single RDS deployment. One of the most important aspects of running multi-az is the fact that if one of the AZ in a region goes down, the production application traffic is automatically routed to the RDS in the alternate AZ. Also, DB maintenance and upgrades are applied to the RDS per AZ basis (for a multi-AZ RDS) without impacting uptime.

With respect to cost, it is totally up to the nature of the application as to how much is the degree of downtime tolerance that it can sustain. It's a cost vs uptime trade-off.

Ivan Aracki
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A Null Pointer
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    Thanks. So I guess the real question here is: what downtime should I expect from a single AZ instance? – UriP Sep 02 '14 at 14:24
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    That is completely subjective. If you experience fatal DB crashes, it might be long before you can rebuild it again and resume service, long can be few minutes to hours depending on how quickly you can restore from a snapshot which again depends on the size of the DB really. Moreover, RDS maintenance windows usually lasts few minutes during which there might be service fluctuations (downtime), so a single AZ deployment might actually feel the effect. – A Null Pointer Sep 02 '14 at 14:44
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    Two additional considerations: First, if your single-AZ RDS database is in the same AZ as your single-AZ production environment, then "high availability" is not really affected: if the AZ that hosts your database in RDS goes down, your application will be down anyway since your application lives in the same AZ (only). Second, restore time to a previous point-in-time even in the multi-AZ setup is often several hours. Hence, a single-AZ RDS database which is frequently backed up to S3 (or to an external service like rsync.net) may be sufficient for some production uses. – Ville Jun 06 '15 at 04:09
  • Thank you, Ville. This was the exact answer I was looking for and suspected for my use case (a very small non-essential WordPress based site). – Matt van Andel Jul 05 '15 at 20:20
  • @MattvanAndel couple years passed, would you mind sharing your experience with the single-az? – Daniel Jeney Aug 15 '22 at 11:28
  • @MattvanAndel Further to Daniel Jeney's question, I'm also interested to know if the choice of Single AZ worked out for you? – Elliveny Oct 02 '22 at 10:27