Earlier quoted context omitted.
this is where docker and the ecosystem around it starts filling in the pieces. also, it makes failures hurt less, and rollbacks much easier.
Docker answers half of the issues: deployment. The other halves: distributed logging (how do you trace a 'transaction' that is being executed against multimachines/multiplaths?) What about rolling releases? what about versioning? What about service discovery (still immature field, look at how many products/tools out there trying to be THE service discovery choice).
We solved the service discovery problem by simply using DNS. Every service runs behind an (internal) Elastic Load Balancer, and we let the load balancer configuration figure out which instance is up and which one is down. Again, not the perfect solution, but it works great for now and is very easy to setup/maintain.