It should not be surprising to anyone that long-established protocol standards are capable and versatile. DNS and LDAP are robust tree-structured replicated at

It should not be surprising to anyone that long-established protocol standards are capable and versatile. DNS and LDAP are robust tree-structured replicated attribute stores; mix in Kerberos for a complete foundation of general purpose directory services. NNTP supplies a straightforward Gossip protocol for eventually-consistent distributed pub/sub. MQTT is still good for lightweight telemetry. I have services I authenticate with via Lamport's mostly forgotten scheme (S/KEY). And so on. There is a current fad of HTTP+JSON as a generic protocol substrate, but it's almost always a mediocre fit for the problem at hand. Go read the RFC archives, there's diamonds to be found. On the other hand, and perhaps even by the same token: using EC2 metadata isn't a completely terrible idea if it's the infrastructure you already have and the semantics line up with specific needs.