GCE Network Interfaces and External IP Addresses

Fault tolerance with Traffic IP Groups in a GCE environment requires the use of External IP addresses. GCE associates External IP addresses to Traffic Managers through adding additional network interfaces to the host. For each External IP address, you require one extra network interface to be attached to your Traffic Manager virtual machine. This is in addition to the first network interface which is reserved for Traffic Manager administration and management. Thus, to use 3 External IP addresses with your Traffic Manager, you require a total of 4 network interfaces to be added when you first create the host virtual machine.

GCE supports a maximum of 8 network interfaces per instance. Therefore, with a single interface reserved for management use, the Traffic Manager can use a maximum of 7 further network interfaces.

Only one External IP address can be associated per network interface. Network interfaces that already have an External IP address association (static or ephemeral) are not used by the Traffic Manager for Traffic IP Groups. If a Traffic Manager is already included in a Traffic IP Group for a Traffic IP Address raised on another instance in the cluster, an interface on the local Traffic Manager is considered reserved for use by that Traffic IP Group in case it is required for failover. Therefore, that interface cannot be used by a different Traffic IP Group.

ATTENTION Traffic Manager virtual machines automatically configure network interface policy routing and rules at startup. For Traffic Manager software variants running on a virtual machine host, you must manually configure policy routing for secondary network interfaces on the host. See the Google Cloud documentation for "Configuring Policy Routing" at https://cloud.google.com/docs for more details.