First of all, be aware that you’re using non stable software, so there can be major changes between releases and unexpected behaviour.
Edit: Is not in development anymore, stable release launched April 19, 2018
Secondly, you cannot ping directly your container, it’s in other net, but you can easily use another container to ping him.
mysql 8 uses caching_sha2_password as the default authentication plugin instead of mysql_native_password. More info here.
Many mysql drivers haven’t added support for caching_sha2_password yet.
If you’re having problems with it, you can change to the old authentication plugin with something like this:
docker run -p 3306:3306 --name mysql_80 -e MYSQL_ROOT_PASSWORD=password -d mysql:8 mysqld --default-authentication-plugin=mysql_native_password