Redundancy Group 0: Routing Engines

When you initialize a device in chassis cluster mode, the system creates a redundancy group referred to in this chapter as redundancy group 0. Redundancy group 0 manages the primacy and failover between the Routing Engines on each node of the cluster. As is the case for all redundancy groups, redundancy group 0 can be primary on only one node at a time. The node on which redundancy group 0 is primary determines which Routing Engine is active in the cluster. A node is considered the primary node of the cluster if its Routing Engine is the active one.

The redundancy group 0 configuration specifies the priority for each node. Redundancy group 0 is primary, and the Routing Engine is active on the node with the higher priority. By default, both nodes have the same priority for redundancy group 0, but you can change the default setting to specify which node is primary for redundancy group 0. Here is how redundancy group 0 primacy is determined:

• If both nodes of a cluster are initialized at the same time and you have not changed the default setting for redundancy group 0 node priority, node 0 takes precedence.
• If you have not changed the default setting for redundancy group 0 node priority and one node of the cluster is initialized before the other, the first node to be initialized takes precedence. In this case, the Routing Engine on the first initialized node is the active one and the node is considered primary. (The primary node is not necessarily node 0. If you boot node 1 before node 0, node 1's Routing Engine takes precedence.)

  The other node is considered secondary. The secondary node's Routing Engine is synchronized with state information from the primary node so that it is ready to take over if the primary node fails.

• If you set the redundancy group 0 node priority, the Routing Engine on the node with the higher priority takes precedence.

  Note: In addition to redundancy group 0, on J-series chassis clusters you configure other redundancy groups that manage the interfaces of the cluster nodes (only one such redundancy group supported on SRX-series chassis clusters). If all these redundancy groups fail over from one node to the other, the node whose redundancy group 0 group is currently primary remains the primary node. The node whose Routing Engine is active is always the primary node.

You cannot enable preemption for redundancy group 0. If you want to change the primary node for redundancy group 0, you must do a manual failover.

Caution: Be cautious and judicious in your use of redundancy group 0 manual failovers. A redundancy group 0 failover implies a Routing Engine failover, in which case all processes running on the primary node are killed and then spawned on the new primary Routing Engine. This failover could result in loss of state, such as routing state, and degrade performance by introducing system churn.

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