certbot-auto uses /etc/issue and various /etc/*release files to determine the system it’s on. On Amazon Linux 2, certbot-auto doesn’t recognize the layout as it has changed from previous versions.
I’ve included instructions of how to make certbot-auto try installation on Amazon Linux 2 below, however, if you’re able to enable the EPEL7 repo as this article suggests, I’d encourage you install Certbot from there. Recent versions of Certbot are packaged in EPEL7 and using this repository should be preferred over certbot-auto.
If you want to use certbot-auto though, the problem is that previously for Amazon Linux /etc/issue contained the string “Amazon Linux” but it doesn’t anymore. To make certbot-auto try the Amazon Linux bootstrapping, you can add “Amazon Linux” to /etc/issue or create the file /etc/redhat-release. Red Hat and Amazon Linux bootstrapping are identical.