One may want to use ssh key types other than "rsa", for example "ecdsa" type for security reasons etc.

The problem is that "ecdsa" key type is not supported by libssh2 - https://libssh2.org/ - Hostkey Types: ssh-rsa, ssh-dss

While zabbix doc suggests to create "rsa" key type, it's not clear that other key types will not work.

Would be nice to add a note:
key types other than "rsa" may be supposrted by "ssh-keygen" tool and ssh servers but they maybe not supported by libssh2, used by zabbix.
Here https://www.zabbix.com/documentation/3.0/manual/config/items/itemtypes/ssh_checks