:Introduction to RDS Custom networking

Manually create the script and configure it to run on startup

1. Create the rds_custom_init.sh script in the /etc folder. The script content is as follows:

   rds_custom_init.sh script

   #!/bin/bash
   echo "RDS CUSTOM INIT START, $(date)" >> /tmp/rds_custom_init.log
   flag=0
   for ((i=1; i<=5; i++)); do
       eth1_ip=$(ip address show eth1 | grep "inet " | awk "{print \$2}" | cut -d'/' -f1)  
       if [[ -n "$eth1_ip" ]]; then
           break
       else
           sleep 1
       fi
   done
   eth0_gateway=$(ip route | grep "default via " | grep "eth0" | awk "{print \$3}")
   # check eth0_gateway
   if [ -z "$eth0_gateway" ]; then
       if [ -f /etc/eth0_gateway ]; then
           eth0_gateway=$(cat /etc/eth0_gateway)
       else
           echo "No gateway found for eth0, and /etc/eth0_gateway file does not exist." >> /tmp/rds_custom_init.log
           exit 0
       fi
   fi
   if [ -z "$eth1_ip" ] && ip address show | grep -q "eth1"; then
       if lsb_release -a 2>/dev/null | grep -q -e "Ubuntu 16.04" -e "Debian"; then
         sed -i 's/eth0/eth1/g' /etc/network/interfaces
         echo "auto eth0" >> /etc/network/interfaces
         echo "iface eth0 inet dhcp" >> /etc/network/interfaces
         sudo systemctl restart networking
         flag=1
         echo "UP ETH1 FOR UBUNTU 16.04 or Debian, $(date)" >> /tmp/rds_custom_init.log
       else   
         HWADDR=$(ip address show eth1 | grep "link/ether" | awk "{print \$2}")
         echo -e "DEVICE=eth1\nBOOTPROTO=dhcp\nONBOOT=yes\nTYPE=Ethernet\nUSERCTL=yes\nPEERDNS=no\nIPV6INIT=no\nPERSISTENT_DHCLIENT=yes\nHWADDR=$HWADDR\nDEFROUTE=yes" | tee /etc/sysconfig/network-scripts/ifcfg-eth1 > /dev/null
         service network restart
         echo "UP ETH1, $(date)" >> /tmp/rds_custom_init.log
       fi
   fi
   eth1_ip=$(ip address show eth1 | grep "inet " | awk "{print \$2}" | cut -d'/' -f1)
   if [ "$flag" -eq 0 ] && lsb_release -a 2>/dev/null | grep -q "Ubuntu 16.04"; then
     sudo systemctl restart networking
     echo "UP ETH1 FOR UBUNTU 16.04, $(date)" >> /tmp/rds_custom_init.log
   fi
   if [ -n "$eth1_ip" ]; then
       ip route add 100.100.0.0/16 via $eth0_gateway dev eth0 2> /dev/null
       keep_route="100.100.0.0/16 via $eth0_gateway dev eth0"
       routes=$(ip route | grep "dev eth0")
       echo "$routes" | while read -r route; do
         if [[ "$route" != "$keep_route" ]]; then
           prefix=$(echo "$route" | awk "{print \$1}")
           ip route delete $prefix dev eth0 > /dev/null
         fi
       done
       echo "DELETE IP ROUTE FOR ETH0, $(date)" >> /tmp/rds_custom_init.log
       eth1_gateway=$(ip route | grep "default via " | grep "eth1" | awk "{print \$3}")
       if ip route | grep -q "100.100.2.136 via $eth1_gateway dev eth1"; then
         ip route delete 100.100.2.136 via "$eth1_gateway" dev eth1
       fi
       if ip route | grep -q "100.100.2.138 via $eth1_gateway dev eth1"; then
         ip route delete 100.100.2.138 via "$eth1_gateway" dev eth1
       fi
       ip route add 100.100.2.136 via $eth1_gateway dev eth1 2> /dev/null
       ip route add 100.100.2.138 via $eth1_gateway dev eth1 2> /dev/null
       ip route delete default via $eth1_gateway dev eth1 2> /dev/null
       ip route add default via $eth1_gateway dev eth1 metric 0 2> /dev/null
   fi
   echo "RDS CUSTOM INIT FINISHED, $(date)" >> /tmp/rds_custom_init.log

2. Run the chmod a+x /etc/rds_custom_init.sh command to grant execute permissions to the script.

3. Edit the /etc/rc.local file to configure the rds_custom_init.sh script to run on startup.

   • If the operating system is not Ubuntu, add /etc/rds_custom_init.sh to the /etc/rc.local file and grant the required permissions to the /etc/rc.local file.

     chmod 777 /etc/rc.local

   • If the operating system is Ubuntu, configure and enable the rc-local.service service.

     1. Edit the /lib/systemd/system/rc-local.service file and add the following content:

        [Install]
        WantedBy=multi-user.target

     2. Configure the rc-local.service service to run on startup.

        # Configure the service to run on startup.
        systemctl enable rc-local.service
        # Check whether the service is configured to run on startup.
        systemctl is-enabled rc-local.service

     3. Start the rc-local.service service.

        # Start the service. 
        systemctl start rc-local.service
        # Check the service status.
        systemctl status rc-local.service

     Note

     Ubuntu 20.04, 22.04, and 24.04 support automatic configuration for attached secondary ENIs by default. If automatic configuration fails, perform the following steps to manually configure the ENI.

     Manual configuration steps

     1. Run the following command to open the secondary ENI configuration file.

        vi /etc/netplan/eth1-netcfg.yaml

     2. Add the following configuration for the secondary ENI to the network interface configuration file, and then save and close the file.

        network:
          version: 2
          renderer: networkd
          ethernets:
            eth1:
              dhcp4: yes
              dhcp6: no

     3. Run the following command to apply the configuration.

        netplan apply