EC2 instance unexpectedly reboots itself

Hi,

As described on the following Knowledge Center page, an EC2 instance could be restarted due to multiple reasons, I recommend you take a look.

If this is the first time it has happened, I would start checking if it is due to a scheduled event, in which AWS restart the instance when must perform tasks such as installing updates or maintaining the underlying host. In this case, AWS sends an email to the email associated with the AWS account prior to the scheduled event, providing details about the event, including the start and end date, but also sends an AWS Health event.

You could also check the system logs at /var/log/messages or /var/log/syslog depending on your OS, to rule out that it is due to operating system-level issues.

On the other hand, If the restarts are frequent, I would review if the health check are failing due to over-utilization of its resource, for which the following Knowledge Center page could be helpful.