Thats my current config, but checking
They are going to Ember, and it’s proxying to the rails port.
Don’t ask 
(educational stuff though debugging the pipeline!).
Useful avenues to check. Was just curious how the OP got on.
I will report my findings for the benefit of others doing crazy configs.
Update:
Ooops, this is where I think I’ve messed up!!
I forgot to add the additional plugins to both containers…