Raft is a consensus protocol. You don't need it if you don't need consensus.
You can do service discovery etc with gossip protocols. You are right that you don't need consensus to have systems publish their own keys on a network.
Systems that use Raft or equivalent do have a need for consensus, for example CassandraDB/CockroachDB (when you do `UPDATE account SET balance = balance - 10 WHERE user='chatmasta';`, you need that transaction to go through only once globally, and you need the whole system to agree on whether it did), Kubernetes (when you ask for a database to be served on some hostname, you need a single instance to go up, and every load balancer to route to that same instance), etc.
If you have examples of systems that use strong consensus when it's not required, point them out. Stating "why do some systems use strong consensus when other systems (doing something completely different) get by without consensus" is a bit strange.
Comments
Raft is a consensus protocol. You don't need it if you don't need consensus.
You can do service discovery etc with gossip protocols. You are right that you don't need consensus to have systems publish their own keys on a network.
Systems that use Raft or equivalent do have a need for consensus, for example CassandraDB/CockroachDB (when you do `UPDATE account SET balance = balance - 10 WHERE user='chatmasta';`, you need that transaction to go through only once globally, and you need the whole system to agree on whether it did), Kubernetes (when you ask for a database to be served on some hostname, you need a single instance to go up, and every load balancer to route to that same instance), etc.
If you have examples of systems that use strong consensus when it's not required, point them out. Stating "why do some systems use strong consensus when other systems (doing something completely different) get by without consensus" is a bit strange.