How to configure Floating IP on Ubuntu

When you attach a new floating IP, you can find it listed to one of the servers at your UpCloud Control Panel that the floating IP currently points to. However, using the new floating IP will require some manual setup. Follow the steps below on how to get this done on Ubuntu servers.

As an example, we have a Cloud Server with the public IP address 185.20.139.167, a floating IP 185.20.139.29, with a netmask 255.255.255.255.

Before making changes to your network configuration, it’s always a good idea to take a backup. Also, note that if your network configuration becomes inoperable, remember that you can always log in to your Cloud Server using the console connection.

Configuring floating IP

Firstly, you’ll need to configure the servers at the OS level, so start up your Cloud Server at your UpCloud Control Panel 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, see the example below.

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 6e:d7:1b:bf:5a:b0 brd ff:ff:ff:ff:ff:ff
    altname enp0s3
    altname ens3
    inet 185.20.139.167/22 metric 100 brd 185.20.139.255 scope global dynamic eth0
       valid_lft 86309sec preferred_lft 86309sec
    inet6 fe80::6cd7:1bff:febf:5ab0/64 scope link
       valid_lft forever preferred_lft forever

Now, to enable the floating IP, add it as an alias to the network interface eth0 that has your public IP address.

Ubuntu uses netplan to configure network interfaces.

Create the following file in the netplan configuration directory with the command below.

sudo nano /etc/netplan/99-floating-ip.yaml

network:
    version: 2
    renderer: networkd
    ethernets:
        eth0:
            addresses:
                - 185.20.139.29/32

Then save the file and exit the editor.

Restrict the file's permissions so that only root can read it.

sudo chmod 600 /etc/netplan/99-floating-ip.yaml

Lastly, apply the changes with the following command.

sudo netplan apply

Afterwards, you should be able to see the floating IP attached to the eth0 network interface.

ip addr

2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 6e:d7:1b:bf:5a:b0 brd ff:ff:ff:ff:ff:ff
    altname enp0s3
    altname ens3
    inet 185.20.139.29/32 scope global eth0
       valid_lft forever preferred_lft forever
    inet 185.20.139.167/22 metric 100 brd 185.20.139.255 scope global dynamic eth0
       valid_lft 86398sec preferred_lft 86398sec
    inet6 fe80::6cd7:1bff:febf:5ab0/64 scope link
       valid_lft forever preferred_lft forever

Applying the changes should not cause you to disconnect from the server.

In case you do lose 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 process to add the alias on any other servers you wish to use the floating IP on.

Testing the configuration

Your configuration is now complete. You can test that it works by transferring the floating IP from one server to another.

First, ping the cloud server or attempt to connect to your server through the floating IP via SSH. Alternatively, if you have a web server configured, open the floating IP on your web browser.

Then transfer the floating IP to another cloud server you’ve configured. This can be done either at your UpCloud Control Panel or by using the UpCloud API.

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

When 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 netmask correctly, and that your firewall isn’t blocking your connections, or try another method to connect.

Using your new floating IP

You can now transfer the floating IP between your cloud servers at your UpCloud Control Panel or by using the UpCloud API!

Depending on your intended use case for the floating IP you may wish to continue by setting up automated load balancing, but it’s always possible to manually transfer the traffic between your servers.