Instance stops every two hours aproximatelly

You can create a CloudWatch alarm when an instance fails its status check https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/monitoring-system-instance-status-check.html#creating_status_check_alarms

As to why it's happening, installing CLoudWatch Agent would give you more detailed metrics to start on your troubleshooting https://repost.aws/questions/QUWmyZXUGlSWScKtu8kRiZFw/instance-stops-every-two-hours-aproximatelly

One place to start looking at is the system load, what is the instance type? To start off the system may appear to run fine with four Wordpress sites, but consumption may rise gradually until a key resource like CPU or memory is exhausted (I'm not saying this is happening, this is just a guess based on what I've seen before). The metrics from CloudWatch Agent should help to confirm this, and it may end up being that the instance type needs to be uplifted to one with more CPU and memory, or if it's just memory you may be able to get away with merely adding more swap space.

Thank you, I will install the cloudwatch, to monitor closely. However, the instance does not fail, it just shuts down, that is why I wanted an alarm for shut-off rather than fail. And the CPU and Memory look good they dont seem to be exhausted. I will follow your advice, to see if I get to the bottom of this.