Are both a gazebo node and an ignition node needed for gazebo8?

edit

Thanks for the question. A gazebo node and an ignition node are both not required for gazebo8, depending on your use case. The same is true for the upcoming gazebo9 release.

Ignition transport will become the future communication protocol used by Gazebo, but it's use is generally not mandatory and most of Gazebo8&9 still uses Gazebo's internal communication protocol.

There are a few places where Ignition Transport is used inside Gazebo8. One example is by the Plotting Widget. Unless you are customizing this widget, then this shouldn't affect you. Another example are VisualizationMarkers. In this case, you could need both an Ignition Node and a Gazebo Node if you are writing a custom plugin/application that needs both visualization markers and communication with other aspects of Gazebo.

The above two examples are new features, and the use of Ignition shouldn't break existing code. It will introduce a bit of a burden as we transition. This is unavoidable, and we are trying to make the impact as minimal as possible.

We are planning to replace Gazebo's communication protocol with Ignition, but this transition will use a tick-tock model. For example, any topic replacement will first have an optional ignition alternative (enabled via a command line argument). The optional ignition topic will then transition to the default, and the gazebo topic will become optional. Finally, the gazebo topic option will be removed. Each step will happen at major releases, which means a single topic replacement would take three years at minimum.

We are working on a migration guide, which should be published before the next Gazebo release in January 2018.