The general answer to this is Byzantine consensus, which cryptocurrency blockchains are designed to solve. If your nodes are willing to fail a little more polit

The general answer to this is Byzantine consensus, which cryptocurrency blockchains are designed to solve. If your nodes are willing to fail a little more politely (e.g. no lying, immediately crashing, etc) you can use something cheaper like raft/paxos. But yeah, it's a lot cheaper to build a reliable system than it is to be resilient.