Related: I don’t plan to doing this right away, but hypothetically: if I had to install two Caddy nodes serving the same hosts, (say, with DNS based load balancing), is there a private key for LetsEncrypt that I need to sync between the nodes?
Not really, but beware that putting Caddy behind a load balancer can cause the challenges to fail. You’re better off using the DNS challenge in that case (so that the Let’s Encrypt server doesn’t have to contact yours), which Caddy will support in version 0.9.