[yocto] How to disable dropbear start on boot

[Bastian Ruppert]

Hello,

we have a Yocto 2.2 image with image-feature read-only-rootfs and ssh-server-dropbear.
On every boot dropbear starts and generates  keys in /var/lib/dropbear/ .
We like to enable dropbear on demand.

How to disable dropbear start on boot?

And what ist the preferred way to change DROPBEAR_RSAKEY_DEFAULT?
Are there some example dropbear%.bbappend files available?

Thank you very much,

Bastian.