Set up your Secondary Network Interface for Ubuntu 18.04

if you are trying to attache the new network interface for your Ubuntu 18.04 EC2 instance, this post might help you to figure out.

Summary

because of Netplan is new network manager in Ubuntu 18.04, things became different as before, and Netplan looks not supported asymmetric routing for now, that is required you to set static ip address & routes for both interfaces.

Solutions

follow above situation

we have to set a default route by on-link option

/etc/netplan/50-primary.yaml

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses:
       - 192.168.0.5/24
      dhcp4: no
      routes:
       - to: 0.0.0.0/0
         via: 192.168.0.1 # gateway address
         on-link: true
       - to: 0.0.0.0/0
         via: 192.168.0.1 # gateway address
         table: 900
       - to: 192.168.0.5
         via: 0.0.0.0
         scope: link
         table: 900
      routing-policy:
        - from: 192.168.0.5
          table: 900
    eth1:
      addresses:
       - 192.168.1.5/24
      dhcp4: no
      routes:
       - to: 0.0.0.0/0
         via: 192.168.1.1 # gateway address
         on-link: true
       - to: 0.0.0.0/0
         via: 192.168.1.1 # gateway address
         table: 999
       - to: 192.168.1.5
         via: 0.0.0.0
         scope: link
         table: 999
      routing-policy:
        - from: 192.168.1.5
          table: 999

Netplan Commands

to let configurations take effect execute netplan --debug apply

or you can use netplan try, it will setup your configuration with rolling back mechanisms, it will rolling back your last configurations in 120 seconds

References

Reaching a directly connected gateway