Hi Jon,
My first post in n8n at this link Is this workflow doable in n8n?
and as you see in diagram i have to many services to automate by n8n .
The end goal is built microservices automation system.
Indeed i have also two questions 
1- I have primary and secondary API servers for service and if main server is down how workflow will be authenticated against secondary server ?
2- is it applicable to use node authentication as variable ? ( same workflow will trigger by different servers and different authentication )
Best Regards