Netplan renderer transition from NetworkManager to systemd-networkd

Ubuntu 18.04 LTS and subsequent versions utilize Netplan to abstract network configuration via YAML files. A key design decision involves selecting the backend renderer, typically choosing between systemd-networkd for server environments and NetworkManager for desktop or dynamic setups.

When transitioning a production interface from NetworkManager to systemd-networkd to reduce overhead or standardize server behavior, there is uncertainty regarding the coexistence of these renderers. Specifically, the interaction between a global renderer setting and interface-specific overrides can lead to conflicting routing tables or unpredictable interface states if not handled precisely.

• How does Netplan resolve conflicts when a specific interface is assigned to one renderer while the global default is set to another?
• What is the expected behavior for existing DHCP leases when switching the renderer for an active interface?