How do I get roscore to talk to gzserver?

edit

I feel like I'm missing some obvious piece of the puzzle here.

My goal is to get a Turtlebot3 simulation displaying on Gzweb.

I've got Gzweb up, and I've got it talking to Gzserver.

But running roslaunch turtlebot3_teleop turtlebot3_teleop_key.launch for example just makes it spin up its own server which doesn't ever seem to connect back to Gzserver.

I thought it would go

gzweb <--> gzserver <--> roscore (through roslaunch)

But this doesn't seem right?

There's also ROS_MASTER_URI, but that doesn't seem to be picked up by Gzserver, so not sure what thing cares about that ENV var.

Any help would be greatly appreciated, thanks!