EGL support is available in Ignition Fortress!
OpenGL traditionally requires a window. Without a window, OpenGL cannot be used. This implies either X11 or Wayland is installed and running; which can be a problem when running on cloud servers, VMs, embedded devices, and similar environments.
This feature is exclusive of Ogre 2.2. Only Ignition Debian packages include this feature, You just need to install Ignition Gazebo and run the server with the following command:
ign gazebo -s --headless-rendering
You can easily try this feature in a Docker container without NVIDIA support. Hopefully this new feature will help you integrating more test in your CI.