AWS EC2 Connection closed by when trying ssh into instance

Question

Recently I set up a new EC2 instance. The next day I was not able to connect to my instance via ssh. I could connect and disconnect the day before, I am sure I did nothing.

Answer 1

I had this problem and it turned out the PEM file was incorrect. You can check following the instructions in Amazon EC2 Key Pairs - Verifying Your Key Pair's Fingerprint:

If you created your key pair using AWS, you can use the OpenSSL tools to generate a fingerprint from the private key file:

$ openssl pkcs8 -in path_to_private_key -inform PEM -outform DER -topk8 -nocrypt | openssl sha1 -c

If you created your key pair using a third-party tool and uploaded the public key to AWS, you can use the OpenSSL tools to generate a fingerprint from the private key file on your local machine:

$ openssl rsa -in path_to_private_key -pubout -outform DER | openssl md5 -c

The output should match the fingerprint that's displayed in the console.