Packet mode interface failover

Hi,

We have two SRX in packet mode. their are two ISP link connected on per gateway for redundancy.

ISP1 is connected on ge-0/0/0 interface and ISP2 is connected on ge-0/0/1 interface.

Here if ISP1(Primary) down ISP2(Secondary) interface should start communicate. once ISP1 interface come up that should again become primary.

Kindly suggest configuration KB.

Thank you...