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How-to

Add a network interface

Put a running instance on a second network by adding a network interface, then set the interface up in its operating system.

Each interface has its own address on its network, and its own security groups. The instance keeps its first interface, which can't be removed.

Before you start

Add the interface

The CLI and OpenTofu create the interface with the security groups you choose. The portal gives a new interface the project's default group.

  1. In the Breqwatr Cloud Portal (Strata), open Instances and choose the instance.
  2. In Networks, choose Attach network.
  3. Pick the Network and choose Attach. The new interface appears in Networks with its address.

The Attach network dialog on web-01's page, with data-net chosen as the network and an Attach button

The new interface has only the default security group. Attach security group in Security groups adds a group to every interface on the instance, but lists only groups the instance doesn't have yet. To give the new interface a group the instance already has, use the CLI, with the interface's port from openstack --os-cloud <cloud-name> port list --server web-01:

openstack --os-cloud <cloud-name> port set --no-security-group --security-group web <port-id>

That replaces the interface's groups with web. Without --no-security-group, it adds web to the groups the interface has.

Create the interface, as a port with its security groups, then add it to the instance:

openstack --os-cloud <cloud-name> port create web-01-data --network data-net --security-group web
openstack --os-cloud <cloud-name> server add port web-01 web-01-data

openstack server add network web-01 data-net also works, and gives the interface the default group, as the portal does.

resource "openstack_networking_port_v2" "web_01_data" {
  name               = "web-01-data"
  network_id         = openstack_networking_network_v2.data.id
  security_group_ids = [openstack_networking_secgroup_v2.web.id]
}

resource "openstack_compute_interface_attach_v2" "web_01_data" {
  instance_id = openstack_compute_instance_v2.web_01.id
  port_id     = openstack_networking_port_v2.web_01_data.id
}

Set it up in the operating system

If the second network has a router, its DHCP offers a default gateway too, and the instance can end up with two routes to the internet. Keep the first interface's: the steps below do that. A network with no gateway, as in A network with no internet, offers no route, so there's nothing to keep.

On Ubuntu, the new interface stays down until you configure it, and a restart doesn't change that. Find its name, the one with no address:

ip -br addr

Then create /etc/netplan/60-second-interface.yaml, with the interface's name in place of ens7:

network:
  version: 2
  ethernets:
    ens7:
      dhcp4: true
      dhcp4-overrides:
        use-routes: false

use-routes: false takes the address from DHCP but not the routes. Apply it:

sudo chmod 600 /etc/netplan/60-second-interface.yaml
sudo netplan apply

The setting is kept across restarts. Other distributions configure interfaces with their own tools.

Windows gets the new interface's address from DHCP on its own. Restart the instance once first: Windows names the interface again at that restart, and forgets settings made before it. Then, in PowerShell as Administrator, find the interface by its address:

Get-NetIPAddress -AddressFamily IPv4 | Format-Table InterfaceAlias, IPAddress

If the network has a router, make Windows prefer the first interface's route, with the new interface's alias in place of Ethernet:

Set-NetIPInterface -InterfaceAlias "Ethernet" -InterfaceMetric 100

Windows uses the route with the lower metric, and the setting is kept across later restarts.

Remove an interface

In Networks on the instance's page, choose Detach on the interface's row, type CONFIRM and confirm. The first interface, marked Primary, has no Detach.

openstack --os-cloud <cloud-name> server remove port web-01 web-01-data
openstack --os-cloud <cloud-name> port delete web-01-data

Remove both resources and apply.

Remove the interface's configuration from the operating system too: on Ubuntu, delete the netplan file and run sudo netplan apply.

Check it worked

  • openstack --os-cloud <cloud-name> port list --server web-01 -c "Fixed IP Addresses" lists an address on each network.
  • In the instance, ip -br addr on Linux, or Get-NetIPAddress on Windows, shows the new address.
  • An instance on the second network reaches the new address, on a port the interface's security groups allow.
  • The instance still reaches the internet through the first interface.