Clean Backups Using Windows Server Backup and EBS Snapshots
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- Simon Waight
One of the powerful features of AWS is the ability to snapshot any EBS volume you have operating. The challenge when utilising Windows 2008 R2 is that NTFS doesn't support point-in-time snapshotting which can result in an inconsistent EBS snapshot. You can still create a snapshot but it may be that one or more file that was mid-change may not be accurate (or usable) in the resulting snapshot.
How to solve
The answer, it turns out, is fairly easy (if a little convoluted) - Windows Server Backup PLUS EBS snapshots.
In order for this to work you will need:
Windows Server Backup installed on your Instance (this does not require a reboot on install).
An appropriately sized EBS volume to support your intended backup (see the Technet arcticle on how to work out your allowance - remember you can always create a new volume later if you get the size wrong!)
Windows Task Scheduler (who needs Quartz or cron ;)).
Some Powershell Foo.
Volume Shadow Copy using the new EBS Volume
Once you have created your new EBS volume and attached it to the Instance you want to backup, open up Windows Server Backup and select what you want to backup (full, partial, custom - to be honest you shouldn't need to do a "bare metal" backup....) Note that Windows Server Backup will delete *everything* on the target EBS volume and it will no longer show up in Windows Explorer - it will still be attached and show up in Disk Manager, but you can't copy files to or from it.
The benefit of Windows Server Backup is that it will utilise Windows Volume Shadow Copy Service (VSS) resulting in a clean copy of files - even those in-flight at the time of backup. This gets around the inability to "freeze" NTFS at runtime.
Set your schedule and save the backup.
Snapshot the backup volume
Now you have a nice clean static copy of the filesystem you can go ahead and create an EBS snapshot. The best way I found to schedule this was to use some Powershell magic written by the guys over at messors.com. I slightly modified the Daily Snapshot Powershell to snapshot a pre-defined Instance and Volume by calling the CreateSnapshotForInstance function that takes an Instance and Volume identifier. The great thing with this script setup is it auto-manages the expiry of old snapshots so my S3 usage doesn't just keep on growing.
I invoke this Powershell on the success of the initial Windows Server Backup scheduled task by using the Task Scheduling - see this post at Binary Royale on how to do this (they send an email - I use the same approach to do a snapshot instead).
The great thing about the Powershell is that it will send you an email once completed - I have also setup mail notifications at completion of the Windows Server Backup (success, failure, disk full) so I can know when / if the backup fails at an early stage. Note that in Windows Server 2008 R2 you can send an email right in Windows Task Scheduler - on AWS you'll need to have an IIS smart host up and running to support this though - see my earlier post on how to set up a IIS SES relay host.
The benefit of this approach is a consistent state for your backup contents as well as an easy way to do a controlled restore at a later date ("create volume from snapshot" in the AWS management console and then attach to an Instance). Additionally you achieve a reasonably reliable backup for not much more than the cost of EBS I/O and S3 I/O and storage costs.
Hope you find this useful.