GATEWAY_IFACE not implemented in netplan and networkd network backends

[jsfrerot]

GATEWAY_IFACE was introduced in 2014 to allow users to designate which NIC should carry the default route when multiple NICs with gateways are defined (originally tracked in https://dev.opennebula.org/issues/2927 and implemented in OpenNebula/addon-context-linux#2).

The feature was implemented for the interfaces (ifupdown/Debian) and rhel backends, but was never ported to the netplan and networkd backends which are now the standard on modern distributions (Ubuntu 18.04+, Debian 12+).

Affected backends:

• netcfg-netplan — no GATEWAY_IFACE handling in gen_routes()
• netcfg-networkd — no GATEWAY_IFACE handling

Environment

• one-context version: 7.0.1
• OS: Ubuntu 24.04 (uses netplan backend)
• OpenNebula: 7.0.1

To Reproduce

1. Create a VM with 2 NICs, each on a different network with a gateway defined
2. Set GATEWAY_IFACE="ETH0" in the VM context
3. Boot the VM
4. Run ip r — both NICs have a default route despite GATEWAY_IFACE being set

default via 10.211.8.1 dev enp3s0 proto static
default via 10.211.80.1 dev enp4s0 proto static

Expected Behavior

Only the designated interface (ETH0) should have a default route:

default via 10.211.8.1 dev enp3s0 proto static
10.211.80.0/22 dev enp4s0 proto kernel scope link src 10.211.80.22

Suggested Fix

In netcfg-netplan, the gen_routes() function should check GATEWAY_IFACE before adding a 0.0.0.0/0 route:

  # Only add default route if this interface is the designated gateway interface
  if [ -n "$gateway" ]; then
      if [ -z "$GATEWAY_IFACE" ] || [ "$(echo $GATEWAY_IFACE | tr '[:upper:]' '[:lower:]')" = "eth${index}" ]; then
          # add default route
      fi
  fi

Same fix should be applied to netcfg-networkd.

References

• Original feature: https://dev.opennebula.org/issues/2927
• Original implementation (interfaces/rhel only): Specify which default gateway to use if there are multiple nics addon-context-linux#2