AWS EC2 Permission Denied (public key) - amazon-web-services

Question

This answer is specifically designed for this type of question, but it has not yet been as clear to me as to its hundreds of upvoters.
I put my key in Downloads. It's found, but it seems like it's not considered a a public key when I use user ubunto. The output is at the bottom of this post. I changed permissions using sudo chmod 600 ~/downloads/mykey.pem but had the same result. I changed permissions using sudo chmod 700 ~/downloads/mykey.pem and had the same result too. From this answer, I tried sudo chown -R me ~/downloads/mykey.pem, then sudo chgrp -R 501 ~/downloads/mykey.pem where uid=501(me).
I have tried ec-2 and root as users without success.
with root as ec-2
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
Permission denied (publickey).
with root as user
skipping output lines
debug1: Trying private key: /Users/me/downloads/mykey.pem
debug1: Authentication succeeded (publickey).
The authentication succeeds, but the connection closes.
skipping output lines
debug1: channel 0: free: port listener, nchannels 2
debug1: channel 1: free: port listener, nchannels 1
Connection to ec2-[myPublicIP].compute-1.amazonaws.com closed.
Transferred: sent 3264, received 2456 bytes, in 10.3 seconds
Bytes per second: sent 316.6, received 238.2
debug1: Exit status 0
Here is the output using user ubunto that the title of this question refers to:
ssh -v -i ~/downloads/mykey.pem -L 60051:localhost:60051 ubunto#ec2-[mypublicIP].compute-1.amazonaws.com
OpenSSH_6.9p1, LibreSSL 2.1.8
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: /etc/ssh/ssh_config line 21: Applying options for *
debug1: Connecting to ec2[mypublicIP].compute-1.amazonaws.com [[mypublicIP]] port 22.
debug1: Connection established.
debug1: key_load_public: No such file or directory
debug1: identity file /Users/me/downloads/mykey.pem type -1
debug1: key_load_public: No such file or directory
debug1: identity file /Users/me/downloads/mykey.pem-cert type -1
debug1: Enabling compatibility mode for protocol 2.0
debug1: Local version string SSH-2.0-OpenSSH_6.9
debug1: Remote protocol version 2.0, remote software version OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.4
debug1: match: OpenSSH_6.6.1p1 Ubuntu-2ubuntu2.4 pat OpenSSH_6.6.1* compat 0x04000000
debug1: Authenticating to ec2-[mypublicIP].compute-1.amazonaws.com:22 as 'ubunto'
debug1: SSH2_MSG_KEXINIT sent
debug1: SSH2_MSG_KEXINIT received
debug1: kex: server->client chacha20-poly1305#openssh.com <implicit> none
debug1: kex: client->server chacha20-poly1305#openssh.com <implicit> none
debug1: expecting SSH2_MSG_KEX_ECDH_REPLY
debug1: Server host key: ecdsa-sha2-nistp256 SHA256:85gcFh6LySYszjod4WIx5wu7BUvKwL4M6EAcZkv0zGw
debug1: Host 'ec2[mypublicIP].compute-1.amazonaws.com' is known and matches the ECDSA host key.
debug1: Found key in /Users/me/.ssh/known_hosts:11
debug1: SSH2_MSG_NEWKEYS sent
debug1: expecting SSH2_MSG_NEWKEYS
debug1: SSH2_MSG_NEWKEYS received
debug1: SSH2_MSG_SERVICE_REQUEST sent
debug1: SSH2_MSG_SERVICE_ACCEPT received
debug1: Authentications that can continue: publickey
debug1: Next authentication method: publickey
debug1: Trying private key: /Users/me/downloads/mykey.pem
debug1: Authentications that can continue: publickey
debug1: No more authentication methods to try.
Permission denied (publickey).

Answer 1

What AMI are you using?
The default user in a stock Ubuntu AMI is ubuntu, not ubunto.
Unless you've created a special AMI that sets up an ubunto user, the user won't exist on the AMI, and hence fail to authenticate.