You have your database instance deployed with AWS and you are using AWS RDS for MySQL. All work smoothly in terms of satisfying queries for your application and delivering reliable uptime and performance. Now you need to take care of your backup strategy. Business is defined to have this retention policy:
- 7 daily full backups
- 4 weekly backups
- 12 monthly backups
Plus the ability to do point-in-time recovery (PITR) for the last 24 hours since the last full backup was taken.
The cloud vendor solution
This is a piece of cake. The daily backups: just set the backup retention period to six days. Done. This also has the plus that PITR is already covered since RDS uploads the transaction logs to S3 every five minutes and stores them in the parquet format, making it smaller than the regular text file. All amazing, right?
Now, the weekly and monthly retention policies are more tricky. But no problem since there is a backup service in AWS called…..AWS Backup. Without going into too much detail, you can create a backup plan for your RDS instance with the desired frequency that suits your retention policies, copy backups between regions for business continuity compliance, etc.
All this comes with a price tag. Let’s do some numbers using the AWS calculator, starting with the snapshots:
According to the documentation “There is no additional charge for backup storage up to 100% of your total database storage for a region.” In other words, this means that one daily snapshot is free. What about the remaining six?
For this example, I will assume the following: a single MySQL RDS instance using m6g.large (the smallest graviton type which is cheaper), Single-AZ, Reserved instance with three years term and paying it upfront. Now, for the disk: a gp2 disk (cheaper than an io1) with a storage capacity of 500GB and I will assume that only half is used.
From the AWS calculator, we have that the monthly cost of the additional backup storage (250GB x 5 days) is $118,75 USD per month or $1,425 USD annually. But that number is not static. Your data most likely will grow. How much will it cost when my data is no longer 250GB but 400GB? The monthly storage cost for the backups could increase to $218 USD, or $2,622 USD annually.
For the PITR, RDS uploads transaction logs to S3 every five minutes. It is not clear if this is charged or not. What it is clear is that in order to restore a DB to a specific point in time, one needs to create a completely new DB instance; you cannot do a PITR over the existing DB, so more costs.
If you are required to distribute your backups for disaster recovery plans or just for business continuity, moving snapshots to a different region comes with a cost depending on the destination region. For example: move to US-EAST-2 (Ohio) comes at a cost of $0.01 per GB. Moving the most recent full daily backup (400GB in our case) will cost $4 USD, which annually means $1,460 USD.
So far we have only discussed the daily backups made by the RDS snapshot feature. And it sums up to $4,082 USD yearly for only 400GB.
Moving on, above we mentioned that the weekly and monthly backups can be taken care of by AWS Backups service. We are not gonna deep dive into these costs primarily because the AWS calculator does not provide a means to use it for that service. However, it is documented that the storage pricing is $0.095 per GB-Month. Now, assuming the unrealistic scenario where your data size is static at 400GB, at the end of the first 12 months the cost will be $6,400 USD. Adding that to the cost of the snapshots, the grand total is:
$10,482 USD annually
And that is for just one RDS instance, with a fairly small data size (400GB), and is not assuming the cost of the instance itself, which depends on the type of instance and its size. Multiply that for the number of clusters in your environment!
Now, to provide some context of how much money that is, know that having an RDS Graviton MySQL instance of size db.m6g.4xlarge costs a bit more than $6000 and a db.m6g.2xlarge is at around $3000 a year. In other words: the annual cost of your backups is similar to having ON a whole year a server with 8 vCPU and 32GiB of memory AND a server with 32 vCPU with 128GiB of memory.
There are additional costs that we haven’t mentioned like if you want to move your backups to cold storage. Currently, the AWS Backup service doesn’t support cold storage for RDS backups, meaning that you need to take care of that by yourself and pay for the cost of that (additional to the storage cost). And if you want to store your data encrypted with your own KMS key, it comes with an additional cost.
Managing your backups like an expert
Percona is prepared to manage the complete lifecycle of your backups for a fraction of the cost and with additional features and capabilities, like PITR at the item level (you don’t need to restore the whole backup to get just the needed table or the needed rows) and can do it over the same instance, with encrypted backups for the same price, cold storage as part of the lifecycle of your data, and many more features.
Percona Managed Services is a solution from Percona to consider!
Thank you, I learned a few new things.
A few questions:
Answers to your questions:
Hi,
According to my tests with AWS MySQL RDS, snapshots are incremental. As far as there are no DB modifications, there are no additional cost for 10 daily snapshots. I launched db.t4g.micro with 25GB storage and paid $0.48/day until I modified DB.
Good points Daniel, RDS backups can indeed be expensive and there is indeed no clear metric to monitor the sizes.
A couple of notes:
“In other words, this means that one daily snapshot is free. What about the remaining six?”
That is not strictly true as that is the allocated storage (not used storage) and the RDS backups (as all EBS snapshots) are incremental. You can find it in many points in the documentation:
“Furthermore the first snapshot of a DB instance contains the data for the full DB instance. Subsequent snapshots of the same DB instance are incremental, which means that only the data that has changed after your most recent snapshot is saved.”
So have the feeling some of the numbers in the article are on the high side. All that said is not uncommon to see deployments where backup accounts for 30% or more of the overall RDS costs
About “one needs to create a completely new DB instance” that is indeed the case with RDS but not with Aurora, where (interestingly) backup costs (USD/GB) are significantly lower than for RDS.
My experience with Aurora is that you have to restore it to a new instance. You cannot restore backup to an existing instance.
Renato – you’re right, according to my test, snapshots are incremental.