:Introduction to RDS Custom networking

Manually create the script and configure settings for the script to run at startup

1. Create the rds_custom_init.sh script in the /etc directory with the following content.

   The 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 executable permissions to the script.

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

   • For operating systems other than Ubuntu, add /etc/rds_custom_init.sh to the /etc/rc.local file and grant the necessary permissions to /etc/rc.local.

     chmod 777 /etc/rc.local

   • For Ubuntu operating systems, configure and enable the rc-local.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 to start on startup.

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

     3. Start the rc-local.service.

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

     Note

     By default, Ubuntu 20.04, Ubuntu 22.04, and Ubuntu 24.04 support the secondary ENIs that are bound in automatic configuration. If automatic configuration fails, perform the following operations.

     Manual configuration

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

        vi /etc/netplan/eth1-netcfg.yaml

     2. Add the information about the secondary ENI to the configuration file. Then, save and exit the configuration file.

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

     3. Run the following command to apply the configuration:

        netplan apply