An SRX1500 cluster does not have an em1 interface.
https://www.juniper.net/documentation/en_US/junos/topics/reference/general/chassis-cluster-srx-series-node-interface-understanding.html
https://www.juniper.net/documentation/en_US/junos/topics/reference/general/chassis-cluster-srx-series-node-interface-understanding.html
