go/oasis-node/cmd: Add node mode and entity verification

Author: martintomazic

go/oasis-node/cmd/node/node.go

@@ -479,6 +479,20 @@ func NewNode() (node *Node, err error) { // nolint: gocyclo
 	}
 	node.EntityID = entityID
 
+	requiresEntity := config.GlobalConfig.Consensus.Validator
+	switch config.GlobalConfig.Mode {
+	case config.ModeValidator, config.ModeCompute, config.ModeKeyManager, config.ModeObserver:
+		requiresEntity = true
+	}
+
+	if requiresEntity && entityID == nil {
+		return nil, fmt.Errorf("node has no entity configured but expects one")
+	}
+
+	if config.GlobalConfig.Mode == config.ModeClient && entityID != nil {
+		return nil, fmt.Errorf("client node must not have entity configured, try using observer mode instead")
+	}
+
 	// Load configured values for all registered crash points.
 	crash.LoadViperArgValues()