Role Introspection

I’m working with a server that is, for my purposes, set in stone – it will function exactly as it functions. I’d like to be able to run it with a docker swarm, but I need one and only one replica in the cluster to run the initial configuration process.

After this process runs, the servers can be identical, but for the purposes of the first launch, they all need to be able to answer the question “which replica am I”. Is there a good way to answer this requirement?