Does anyone know why rpd would not run on secondary node?
In a Juniper SRX Chassis Cluster, the master Routing Engine (RE) runs on only one node. This creates an active/passive control plane. All control plane processes (rpd, kmd, etc.) run only on the master RE.
The special redundancy group 0 refers to the status of the control plane. In this example, node 0 is the primary node for this group and, therefore, it is in charge of all control plane calculations (it acts as the master RE and runs the control plane processes like rpd, kmd, dhcpd, pppd, and others).