# https://dev.classmethod.jp/cloud/aws/how-to-work-with-amazon-linux2-amazon-linux-extras/
$ amazon-linux-extras help
help See list of commands.
info See details of a specific package.
install Enables specified topics and installs their packages.
list Lists topics in the catalog. Some may be enabled.
Amazon Linux Extras software topics give you access to the most-recent
stable software you specifically choose, without the uncertainty of a
wholly new environment.
Best practice is to enable only one or two topics. More than that, and
you lose the benefits of working in a stable environment.