Configure additional static IP with netplan

It is not advised to overwrite the .yaml file cloud-init created. Instead, we could only list the additional IPs like so:

network:
  version: 2
  ethernets:
    eth0:
      addresses:
        - 10.10.10.2/24

This works because netplan generates config by merging YAML files, and the rules are that sequence values are concatenated, with the new values appended to the old list. See netplan-generate(8) for details.

Alternatively, you could create /etc/cloud/cloud.cfg.d/99-disable-network-config.cfg as follows to prevent cloud-init from changing network configuration again:

network:
  config: disabled

However, this approach would prevent the image to be reused for another instance.