How to convert a gazebo ros system to ignition?

edit

I have a simulation running using gazebo_ros and associated sensor, steering control, and ros_control joint plugins as well as spawn model clients, subscribers to gazebo ros topics like link_states. How do I convert it to use gazebo ignition instead of regular/classic/legacy/old gazebo?

Update

I've did a manual xacro -> urdf -> sdf conversion and launched it in apt installed ignition gazebo 5.1.0 on Ubuntu 20.04 - it launches then exits immediately without error messages. I commented out all plugins and got the same result.

rosrun xacro xacro `rospack find foo`/urdf/foo.xacro > foo.urdf
ign sdf -p foo.urdf > foo.sdf
ign sdf -k foo.sdf 
Valid.
ign gazebo -r foo.sdf

then

cat ~/.ignition/gazebo/log/2021-09-28T07:40:34.139832791/server_console.log
(2021-09-28T07:40:34.208084312) [Msg] Ignition Gazebo Server v5.1.0
(2021-09-28T07:40:34.234733865) [Msg] Loading SDF world file[/home/lucasw/foo.sdf].
(2021-09-28T07:40:34.342594813) [Msg] Serving world names on [/gazebo/worlds]
(2021-09-28T07:40:34.342648561) [Msg] Resource path add service on [/gazebo/resource_paths/add].
(2021-09-28T07:40:34.342675119) [Msg] Resource path get service on [/gazebo/resource_paths/get].
(2021-09-28T07:40:34.342733439) [Msg] Resource paths published on [/gazebo/resource_paths].
(2021-09-28T07:40:34.342751892) [Dbg] [ign.cc:353] Shutting down ign-gazebo-server

Next steps could be to build a newer ignition from source, or create or find working sdf files and modify mine to resemble those working examples until it loads, try to restore one link and joint at a time, enable more verbose/debug output which maybe requires a build flag.