SSH Connection Issue: Unable to Connect to EC2 Instance After Changing Instance Type from t2 to t3

Question

Hello everyone,

I encountered an issue I'm struggling to understand. I have an EC2 instance with a type of t2.micro, and it's working perfectly. However, when I change the instance type from t2 to t3, I can no longer connect to it via SSH. This problem occurs consistently with every t3 instance type I try. Oddly enough, when I switch back to t2 types, SSH connectivity is restored.

I've checked the instance status, and everything appears normal. The instance passes the 2 checks, but I still can't connect. I'm puzzled by this behavior and would appreciate any insights or suggestions. Thank you.

Accepted Answer

T3 is a Nitro-based instance type, T2 is not https://docs.aws.amazon.com/ec2/latest/instancetypes/ec2-nitro-instances.html#nitro-instance-types

I think it would be advisable to read the knowledge document [Why is my Linux instance not booting after I changed its type to a Nitro-based instance type?](https://repost.aws/knowledge-center/boot-error-linux-nitro-instance) and follow the recommended steps.

This also a good third-party explainer https://www.continuent.com/resources/blog/how-convert-aws-instance-family-t2-t3-enhanced-networking-amazon-linux-1

Also, when the instance is up and 2/2 checks passed and you're not able to SSH into it, are you able to connect using AWS Systems Manager Session Manager? https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-prerequisites.html

Answer

Hi,

Some other folks had similar issues in the past and fixed them: https://repost.aws/questions/QUG_Q2Tu0cQemkhTMoISVLtQ/convert-a-t2-instance-to-t3

Best,

Didier

Answer

Thanks for all the assistance! It appears the issue was related to an EBS volume. I had created and attached an EBS volume to the instance when it was a t2 instance, where the volume was mounted as `/dev/xvdf`. However, when changing the instance type to t3, the device name for the EBS volume changed, causing the `fstab` to fail and the instance to enter emergency mode.

Answer

Hi, Please check the below steps and share the status if it doesn't work properly.
1. Please check the inbound ssh port, 22, is opened properly.  
2. Check the DNS is solved at the client.
```
 $ dig 
```

3. EC2 is deployed in a public subnet.

SSH Connection Issue: Unable to Connect to EC2 Instance After Changing Instance Type from t2 to t3

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