Instance reachability check failed (Ubuntu 20.04). Cannot SSH into the instance.

Question

We recently moved from t2.micro to t2.medium. We were able to connect using SSH and work with the instance without any issue. This morning, we observed error connecting using SSH and also found on the console that ***Instance reachability check failed*** for this instance.

The System Log shows many errors. First of which says "Failed to start  Network Time Synchronization" and after that it also shows
OSError: [Errno 30] Read-only file system: '/var/lib/cloud/data' 
Failed to start Network Service
Failed to start Network Name Resolution and so on...

We are unable to connect using EC2 instance connect or EC2 serial console. Any pointers or help will be greatly appreciated.

Answer

Hello.

Have you tried restarting EC2?  
https://repost.aws/knowledge-center/ec2-linux-status-check-failure

Your boot volume may have become corrupted.  
I think it would be a good idea to detach the EBS volume from EC2 and attach it to another EC2, then use the following command to look for errors.  
https://repost.aws/knowledge-center/ec2-linux-emergency-mode

https://stackoverflow.com/questions/52069573/read-only-file-system-on-vagrant-visualbox-ubuntu16-04  
```
sudo fsck -f /dev/sdaX
```

Instance reachability check failed (Ubuntu 20.04). Cannot SSH into the instance.

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