AWS Backup - EC2 AMIs EBS Incremental snapshots

Question

Hi all,
One of our internal teams is using **AWS Backup** to create **AMIs**  for a list of important **EC2 instances** they are running in the **Production environment**. They are using the following backup plan resource assignments :

```
Resource assignment name
    VM_TagBackupTrue
IAM role
    arn:aws:iam::*:role/BackupRole
Assign by ARN prefix
    arn:aws:ec2:*:*:instance/*
Tags - equal
    aws:ResourceTag/backup - true
```

The backup frequency is **daily**, and the retention period is **14 days**.

From what I've gathered from the AWS Documentation, there is no need to add the **EBS Volumes** to the resource assignments because by just adding the "arn:aws:ec2:*:*:instance/*", AWS Backup will create an AMI with a snapshot for the attached volume(s).

My questions are:
1. Every time AWS Backup creates a daily AMI, does it create a full snapshot of the attached volume(s)?
2. If EBS snapshots are incremental, how does this work without conflicting with the 14-day retention period?
3. How is all of this billed ?

Thanks in advance.

Riku_Kobayashi · Accepted Answer

Hello.

> Every time AWS Backup creates a daily AMI, does it create a full snapshot of the attached volume(s)?

I think the snapshots associated with the AMI created by AWS Backup are incremental backups.  
If "Incremental backup" is checked in the table listed in the document below, I think you are using incremental backup.  
Therefore, only the first snapshot created will be a full backup, and from then on, only the parts that have changed will be backed up.  
https://docs.aws.amazon.com/aws-backup/latest/devguide/backup-feature-availability.html#features-by-resource

> If EBS snapshots are incremental, how does this work without conflicting with the 14-day retention period?

EBS snapshots are designed to avoid conflicting.  
I recommend reading the following documentation:  
https://docs.aws.amazon.com/ebs/latest/userguide/ebs-deleting-snapshot.html

> How is all of this billed ?

The first backup will be a full backup, and subsequent backups will be incremental backups, so I think you will be charged for the data that is ultimately saved.  
https://aws.amazon.com/ebs/pricing/?nc1=h_ls

So, assuming that the capacity increases by 1GB per day, I think the calculation will be as follows.  
I thought it would be 39GB on the 30th day, so I would be charged 1.225 USD for that month.  
```
day1: 10GB
day2: 11GB
...
day30: 39GB

39GB * 0.05USD = 1.225USD
```

Leo K · Answer

The answer to your original question is that the snapshots created for the AMIs will be incremental.

The way it works is that when the first snapshot is created of a volume, all the 512-kiB blocks (counted from the beginning of the volume) that have ever been written to at least once will be included in the initial snapshot. That's what makes it a "full" snapshot.

When the next snapshot is made of each volume by the AMI triggered for the EC2 instance the following day, each of those snapshots will only include those 512-kiB blocks that aren't present in any of the earlier snapshots (in this case, the initial, only snapshot made the previous day). For all the 512-kiB blocks that are already contained in the previous snapshot, only a pointer will be included in the new snapshot, pointing to that data block.

When the full 14-day cycle has been completed and the oldest snapshot is deleted, all the data blocks that continue to be referred to by the remaining snapshots will be kept by EBS. Cost-wise, each data block will be charged from the first/oldest snapshot to contain a pointer to it. If any data blocks in the deleted snapshot (the 15-day-old one) are no longer pointed to by any of the remaining snapshots, those "orphaned" blocks will be deleted permanently and no longer charged from your account.

AWS Backup - EC2 AMIs EBS Incremental snapshots

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