[DHCP Relay]: Wait for all interfaces to come up before starting DHCP relay

dockers/docker-dhcp-relay/start.sh

@@ -1,16 +1,41 @@
 #!/usr/bin/env bash
 
+function wait_until_iface_exists
+{
+    IFACE=$1
+
+    echo "Waiting for interface ${IFACE}..."
+
+    # Wait for the interface to come up (i.e., 'ip link show' returns 0)
+    until ip link show $IFACE > /dev/null 2>&1; do
+        sleep 1
+    done
+
+    echo "Interface ${IFACE} is created"
+}
+
+# Create isc-dhcp-relay config file
 sonic-cfggen -m /etc/sonic/minigraph.xml -t /usr/share/sonic/templates/isc-dhcp-relay.j2 > /etc/default/isc-dhcp-relay
 
 rm -f /var/run/rsyslogd.pid
 
 supervisorctl start rsyslogd
 
-VLAN_IFACE_NAME=`sonic-cfggen -m /etc/sonic/minigraph.xml -v "minigraph_vlan_interfaces[0]['attachto']"`
+# Wait for all interfaces to come up before starting the DHCP relay
+
+FRONT_PANEL_IFACES=$(sonic-cfggen -m /etc/sonic/minigraph.xml --var-json "minigraph_interfaces" | grep "\"attachto\":" | sed 's/^\s*"attachto":\s"\(.*\)".*$/\1/')
+for IFACE in $FRONT_PANEL_IFACES; do
+    wait_until_iface_exists $IFACE
+done
+
+VLAN_IFACES=$(sonic-cfggen -m /etc/sonic/minigraph.xml --var-json "minigraph_vlan_interfaces" | grep "\"attachto\":" | sed 's/^\s*"attachto":\s"\(.*\)".*$/\1/')
+for IFACE in $VLAN_IFACES; do
+    wait_until_iface_exists $IFACE
+done
 
-# Wait for the VLAN to come up (i.e., 'ip link show' returns 0)
-until ip link show $VLAN_IFACE_NAME > /dev/null 2>&1; do
-    sleep 1
+PORTCHANNEL_IFACES=$(sonic-cfggen -m /etc/sonic/minigraph.xml --var-json "minigraph_portchannel_interfaces" | grep "\"attachto\":" | sed 's/^\s*"attachto":\s"\(.*\)".*$/\1/')
+for IFACE in $PORTCHANNEL_IFACES; do
+    wait_until_iface_exists $IFACE
 done
 
 # Start the DHCP relay

files/build_templates/dhcp_relay.service.j2

@@ -1,7 +1,7 @@
 [Unit]
 Description=DHCP relay container
 Requires=docker.service
-After=interfaces-config.service
+After=swss.service
 
 [Service]
 User={{ sonicadmin_user }}