Cloud-init provides our device the network configuration at boot.
If we want to configure manually the network, we should disable the network configuration capabilites of Cloud-init so our configuration persist between reboots.
We need co create a configuration file at /etc/cloud/cloud.cfg.d with the instruction to disable it.
You can use the following command, or write it manually instead.
bash -c 'echo "network: {config: disabled}" > /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg'