What happens when you reboot your EC2 instance?
March 5, 2010 | In: AdoMado, Cloud Computing, Startups
We had to answer this question yesterday when our EC2 instance stopped responding and was constantly showing 100% CPU load. SSH wasn’t working and neither was apache responding. The CPU was hung at 100% load for a full day.
Hence, we decided that a reboot was the only solution.
I had a notion (and had read it as well) that a reboot wipes your disk clean and you start from a brand new AMI.
I was wrong. And I’m happy that I was wrong 
We found, rebooting an EC2 instance does not affects your disk state. Your data is preserved.
But, if you terminate the instance and fire it up again, you’ll start form scratch.
Post reboot, we have recovered all our data (it was intact).
Threads to see – here and here.
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View Comments to What happens when you reboot your EC2 instance?
Gaurav
March 5th, 2010 at 5:42 am
had some similar experiences ..had wiped my office date on my colleague machine EC2
still remember that day
Vivek Khurana
March 5th, 2010 at 10:52 am
It is clearly mentioned in the EC2 docs that reboot does not wipes the disk state. Halting your machine will wipe it because machine is deleted when halted.
Btw, Amazon reserved instances preserve data when you halt a machine.
Shlomo Swidler
March 5th, 2010 at 9:06 am
@Vivek Khurana,
Reserved Instances do not preserve anything. Reserved Instances are not really instances – they're a billing feature, giving you a lower hourly rate for any running instance that matches the availability zone and OS and instance type of the reservation. You still need to launch the instances and manage their lifecycles.
You can boot from an EBS-backed AMI. EBS-backed instances can be "stopped" and "started", which allows you to keep them off but intact. The contents of disk are preserved while "stopped", and to the OS it looks like a power off (stopping it) and power on (restarting it).
makuchaku
March 6th, 2010 at 3:01 pm
Next objective… move over to an EBS backed instance!