This article describes about how to troubleshoot the traffic forwarding issue when the interface is bounded to routing instance.
Traffic will reach SRX, however it is not forwarded to the server.
When the external interface is bounded to Routing instance, first thing we need to care about is, to have a route under routing instance.
set routing-instances WAN-RI routing-options static route 20.1.1.1 next-hop 10.1.1.1
Or leak the route from the default instance to the intended routing-instance
Follow the KB16133 [juniper.net] to know about RIB groups which helps to leak routes between routing instance.