AWS EC2 Instance Reachability Check FAILED

I have an issue with one of my EC2 instances in AWS. It was working perfectly for months and I didn't make any changes to instance's setting since the first time I created it. and suddenly I couldn't connect via SSH to it.
I checked the status check from AWS EC2 console and both System System status checks and Instance status checks passed.
I checked the system log and couldn't find anything that can help me identify the issue. I could see the the CPU usage is getting high from monitoring dashboard, and I still couldn't do anything because I can not connect to my instance.

I spent 5 hours to check on internet what could be the solution for the issue. please note that both both System System status checks and Instance status checks passed. and I refreshed the page regularly.
and then suddenly I got "reachability check failed" under instance status check , (what took you so long to notify me this, AWS? ).

this information gave me clue what could be the issue and how to solve it.
I refer to My EC2 Linux instance failed the instance status check due to over-utilization of its resources. How do I troubleshoot this? from AWS knowledge center.

The Solution

Reboot your instance

My EC2 CPU utilization was near 100% , so I tried rebooting the EC2 instance to return it to a healthy status.
and minutes later, everything worked well.
you can refer the the article from knowledge center above it rebooting your instance doesn't solve the issue.

Use a rescue instance

if the first method doesn't solve the issue, you can try use a rescue instance method. Here is the step by step how to follow this method
Launch a new EC2 instance in your VPC using the same Amazon Machine Image (AMI) and in the same Availability Zone as the impaired instance. The new instance becomes your rescue instance.

1. Stop your impaired instance.
2. Detach the EBS root volume from your impaired instance.
3. Attach the EBS volume as a secondary device to the rescue instance.
4. Connect to your rescue instance using SSH.
5. Create a mount point directory (/rescue) for the new volume attached to the rescue instance.
6. Mount the volume at the directory that you created in step 6.
7. Unmount the secondary device from your rescue instance.
8. Detach the secondary volume (/dev/sdf) from the rescue instance. Then, attach it to the original instance as /dev/xvda (root volume).
9. Start the instance and then check if the instance is responsive.

Good Luck