Once you get a confirmation from the UpCloud Support that a floating IP has been added, you can find it attached to one of your servers at your UpCloud Control Panel, but using the added IP will require some manual setup. Follow the steps below to find out how to get this done on a CoreOS server.

Set up static IP addresses

For this example, the server 1 (94.237.33.165) and the server 2 (94.237.33.150) have a common floating IP 94.237.33.180 and a gateway 94.237.32.1.

Next, you need to configure the servers at the OS level, so start up your systems and log in.

Check your current network settings with the following command.

ip addr

Commonly the second network interface card (NIC) named eth0 has your public IPv4 address assigned to it, like in the example output below.

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
   link/ether 6e:d7:1b:bf:20:df brd ff:ff:ff:ff:ff:ff
   inet 94.237.33.165/22 brd 94.237.35.255 scope global eth0
      valid_lft forever preferred_lft forever
   inet6 fe80::6cd7:1bff:febf:20df/64 scope link
      valid_lft forever preferred_lft forever

In addition to the IP addresses, you will need the default gateway, it can be found with the command underneath.

route -n
Kernel IP routing table
Destination  Gateway      Genmask        Flags  Metric  Ref  Use  Iface
0.0.0.0      94.237.32.1  0.0.0.0        UG     0       0    0    eth0
10.0.0.0     10.1.8.1     255.0.0.0      UG     1024    0    0    eth1
10.1.8.0     0.0.0.0      255.255.252.0  U      0       0    0    eth1
94.237.32.0  0.0.0.0      255.255.252.0  U      0       0    0    eth0
172.17.0.0   0.0.0.0      255.255.0.0    U      0       0    0    docker0
172.18.0.0   0.0.0.0      255.255.0.0    U      0       0    0    docker_gwbridge

Set the addresses statically on the NIC with your public IPv4, eth0 in this case. On a CoreOS host, this can be done by creating a network configuration file at /etc/systemd/network.

sudo vi /etc/systemd/network/static.network

Enter the following two sections with the specified details found in the outputs above. The name match defines which network interface the addresses belong to, while the addresses include the normal IPv4 and the floating IP address. For the gateway, use the IP address ending in .1 shown in the Kernel IP routing table for your network interface.

[Match]
Name=eth0

[Network]
Address=94.237.33.165/22
Address=94.237.33.180/22
Gateway=94.237.32.1

After adding in the required details, save the file and exit. You will then need to restart the networking process to enable the static configuration.

sudo systemctl restart systemd-networkd

If you were connected with SSH, the networking restart should not cause you to disconnect. In case you do loose connection and are unable to reconnect, you can always use the web Console at UpCloud Control Panel under your Server settings to go through the setup again to make sure everything is entered correctly.

Repeat the steps on your other server to configure it with static IP addresses as well.

Enabling traffic to the floating IP

With the static IP addresses set up, check which server the floating IP is attached to under the Public network list at your UpCloud Control Panel. The traffic to the floating IP is by default directed to the server it was initially assigned to.

Check your network configuration again with the same command as before.

ip addr

The newly added floating IP should show up under the same NIC as the public IP address.

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
   link/ether 6e:d7:1b:bf:20:df brd ff:ff:ff:ff:ff:ff
   inet 94.237.33.165/22 brd 94.237.35.255 scope global eth0
      valid_lft forever preferred_lft forever
   inet 94.237.33.180/22 brd 94.237.35.255 scope global secondary eth0
      valid_lft forever preferred_lft forever
   inet6 fe80::6cd7:1bff:febf:20df/64 scope link
      valid_lft forever preferred_lft forever

Now attempt to connect to your server using the floating IP with SSH, or if you have a web server configured open the floating IP on your web browser.

If you get a reply, the floating IP works on that server and you can continue forward. If it didn’t work, make sure you entered the IP address and gateway correctly, that your firewall isn’t blocking your connections, or try another method to connect.

Transferring the floating IP

Your configuration should now be working, but a static floating IP would be of a little use. Test that the address can be transferred between the server.

To do this, you will need to tell the gateway which host the traffic coming to the floating IP should be directed to. A simple way to do this is using the arping command line network tool, but it is not installed on the minimalistic CoreOS by default. Fortunately, docker is able to provide the solution with the busybox container image, which includes many useful tools in a small and simple package.

Use the following docker command to run a single arping request.

docker run --network=host --entrypoint=/bin/arping --rm busybox -c 3 -U -s <floating IP> <gateway>

Docker will download the latest busybox image, starts it up attached to the host network and runs the arping command with the parameters after the busybox image name. Replace the <floating IP> and <gateway> with the correct IP addresses for your system and you should see an output similar to the example below.

docker run --network=host --entrypoint=/bin/arping --rm busybox -c 3 -U -s 94.237.33.180 94.237.32.1

ARPING to 94.237.32.1 from 94.237.33.180 via eth0
Unicast reply from 94.237.32.1 [00:00:0c:9f:f0:10] 0.895ms
Unicast reply from 94.237.32.1 [00:00:0c:9f:f0:10] 0.747ms
Sent 3 probe(s) (1 broadcast(s))
Received 2 reply (0 request(s), 0 broadcast(s))

Test the floating IP again with any method you prefer. When you get a connection you have successfully transferred the floating IP.

Using your new floating IP

You can now transfer the floating IP between your cloud servers by running the busybox arping command on the new destination host.

Depending on your intended use case for the floating IP you may wish to continue by setting up automated load balancing, but if you wish to manually transfer the traffic between your servers, it might be useful to create scripts of the required command.