Instance reachability check failed

Question

Hi

In the Instance status checks show "Instance reachability check failed" and I am unable to SSH to the Instance.

The AWS Compute Optimizer was throwing an error in EBS for reading and write bandwidth, so I decided to upgrade the instance from t2.medium to t3.large, also the hard drive from 8GB to 16GB to gp3. Now It shows Running. But in Status checks, Instance status check shows "Instance reachability check failed". The instance was working fine a few days back.

I tried rebooting instance. It doesn't reboot. I start stop and start, that works and shows Running, but same instance status check issue.

I tried rescue option mentioned in https://aws.amazon.com/premiumsupport/knowledge-center/ec2-instance-boot-issues/, but still the same issue.

Here is the system log

`
[   12.483121]  
[   12.485967] Kernel Offset: 0x10600000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
[   12.497046] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000100 ]---
`

Answer

Hi There
Please take a look at this support article, there are several reasons why a Linux instance might fail to start when moving from t2 to t3.

```
Here are some common reasons why a Linux instance might not boot after you change it to a Nitro-based type:

1.The Elastic Network Adapter (ENA) enaSupport attribute is disabled for the instance.
2.The ENA module isn't installed on the instance.
3.The NVMe module isn't installed on the instance, or, if installed, the NVMe module isn't loaded in the initramfs image of the instance.
4.You are trying to mount the file systems at boot time in the "/etc/fstab" file using a device name. Amazon Elastic Block Store (Amazon EBS) volumes are exposed as NVMe devices to these instance types, and the device names are changed. To avoid this, mount the file systems using UUID/Label. For more information, see Amazon EBS and NVMe on Linux instances.
```

https://aws.amazon.com/premiumsupport/knowledge-center/boot-error-linux-nitro-instance/

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Instance reachability check failed

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