Comment 1 for bug 1553113

Here is a deployment graph from TestBlockDeviceDevicesSerialization80 with extended edges colouring.

When we calling _update_dependencies of OrchestratorGraph it is using groups to create dependancies.

If we are supposing that developer have made a mistake and defined roles instead of groups (see refer. bug) we should use roles as groups if no groups provided.

The green connections is the connections created using groups fields.
The red connections created using roles when groups are not found.

As you could see adding red lines (roles) creating loops in this graph making it's proper traversal impossible.

So i don't see easy way of substitution groups dependencies with roles in legacy orchestrator.