SSH key file Naming conventions.

Per ssh defaults, must use "authorized_keys" and "id_rsa" as default files.

For EC2 instances, I use my *Awskp* keys only for setup.
Use my regular personal key to access from Internet after that.
Use *Infra* keys for intra-AWS-network access.

id_rsa  sym-link to default private key
*.rsa  RSA private key     Generic "-----BEGIN RSA|OPENSSH PRIVATE KEY..."
*.dsa  DSA private key     Generic "-----BEGIN DSA|OPENSSH PRIVATE KEY..."
*-rsa.pub RSA public key   Single line "ssh-rsa <ENCODED_KEY> [comment]"
*-dsa.pub DSA public key   Single line "ssh-dss <ENCODED_KEY> [comment]"
*-rsa.ppk  Putty RSA private key   Starts with "PuTTY-User-Key...ssh-rsa"

Notes
With any generic public or private key file that have the "--- LABEL ---"
  delimiter lines, you can put any comments outside of the delimeters.
Putty public files are generic public key files that identifies type as just
"SSH2" instead of the algorithm as is required in SSH authorized_keys.
To convert to a OpenSSH authorized_key record, 3 tokens all on one line:
  <ALGORITHM> <JOINED_ENCODED_LINES> <Any comment at all or none>
For example:
  ssh-rsa AAA...AYJB blaine@admc.com for beyla
OpenSSH private key files are generic public key files that specify algorithm.
authorized_keys does work if it's 0644.
private keys file sym links and authorized_keys link do work.