No DHCP IP on eth0 with Ubuntu Server 26.04 (64-bit) on Raspberry Pi 4b

This week I was attempting to get up and running with Ubuntu Server 26.04 (64-bit) on a Pi 4b using Raspberry Pi Imager 1.8.5. I noticed this same problem both times I went through this process.

I used the option to edit and apply configuration settings in the Raspberry Pi Imager

General Tab:

• Set hostname

• Set username and password

• unchecked Configure wireless LAN

• set locale settings

Services:

• Enable SSH

• Allow Public Key Authentication Only (and pasted in my public key)

Then I flashed the microSD card, booted the Pi with it, watched a lot of stuff go by and then saw that it was trying and failing to reach the Ubuntu repos to update itself. The eth0 interface link light was on and maybe also flashing activity, but the system was unreachable on the network. Logging in on the console showed no assigned IP to eth0 even though /etc/netplan/50-cloud-init.yaml contained:

network:
  version: 2
  ethernets:
    eth0:
      optional: true
      dhcp4: true

In the end, all I had to do was run sudo netplan apply from the console and it picked up its eth0 IP and other info via DHCP.