Recent versions of OpenSSH remove support of ssh-rsa key types and host key algorithms from the default conection configuration. Set options to enable them and provide a configuration option which can disable them if required.
Vagrant Core Plugins
These are plugins that ship with Vagrant. Vagrant core uses its own plugin system to power a lot of the core pieces that ship with Vagrant. Each plugin will have its own README which explains its specific role.
Generate proto
grpc_tools_ruby_protoc -I . --ruby_out=gen/plugin --grpc_out=gen/plugin ./plugin_server.proto