Any speed benefit to using Windows fast launch vs simply skipping sysprep?

Question

We've been building Windows AMIs for temporary CI/CT usage, running "InitializeInstance.ps1 -SchedulePerBoot" before shutdown but not running the sysprep command. We're also skipping setting the computer name and extending the boot volume to minimize startup time as much as possible. We've done this both manually and using Packer; unfortunately last I check this isn't possible with EC2 Image Builder.

Is there any launch speed benefit to using the Windows fast launch AMI option vs doing this? We're still seeing ~8 minute startup times (until operational) with this method.

I don't know what benefit sysprep gives us since the AMI usage is all internal and we're not joining a domain (although I believe even that is fine as long as it's not done pre-imaging).

Answer

Hello there,

Greetings of the day and I hope you are well!

Thank you for contacting AWS RePost. My name is Ankit and I’ll be assisting you.

Windows Fast Launch for AMI is used to create the performance optimized Windows Image, EC2 launches an instance and runs through Sysprep steps, rebooting as required.

Every Amazon EC2 Windows instance must go through the standard Windows operating system (OS) launch steps, which include several reboots, and often take 15 minutes or longer to complete. Amazon EC2 Windows Server AMIs that have the Windows fast launch feature enabled complete some of those steps and reboots in advance to reduce the time it takes to launch an instance. For more information [1]

Amazon EC2 automatically replenishes the snapshots you have on hand as it uses them to launch instances from the Windows fast launch enabled AMI.

Query: Is there any launch speed benefit to using the Windows fast launch AMI option vs doing this? We're still seeing ~8 minute start-up times (until operational) with this method.

Answer : Regarding Windows Fast Launch vs without Sysprep, according to [2] A snapshot of an instance that was launched from a Windows AMI with Windows fast launch enabled, and that has completed the following Windows launch steps, rebooting as required.
	○ Sysprep specialize
	○ Windows Out of Box Experience (OOBE)
	
Sysprep removes unique information from an EC2 Windows instance. This information includes the instance security identifiers (SID), computer name, and drivers. If you wish to create a generic image with unique security identifiers that can be used across multiple server then you can opt for sysprep. For more information, see [3].

When you launch instance by skipping sysprep, instance is booted as backup. Thus, Windows Fast launch AMI is focused on launch instance fast with OOBE [Out-of-box-experience] which will be missing from AMIs that are created by skipping sysprep.

I hope that the given information and action plan is helpful to you.

If you feel we can provide any additional assistance with regard to this matter, I would request you to reach out us by opening a Support Ticket and we can investigate further.

Thank you and Have a great day ahead!

REFERENCES

[1] Configure Windows fast launch for your Windows Server AMI
https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/win-ami-config-fast-launch.html

[2] Configure Windows fast launch for your Windows Server AMI - Key terms
https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/win-ami-config-fast-launch.html#win-fast-launch-key-terms

[3] https://learn.microsoft.com/en-us/windows-hardware/manufacture/desktop/sysprep--system-preparation--overview?view=windows-11

Any speed benefit to using Windows fast launch vs simply skipping sysprep?

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