clock not synced with ntp sometimes breaks apt update

[Ryan Harper]

Using https://releases.ubuntu.com/20.04/ubuntu-20.04.3-live-server-amd64.iso on a server behind firewall which does not have access to ntp.ubuntu.com fails during the install part where curtin runs apt update.

Apt reports error: "Release file is not yet valid"

Looking at the logs, it showed clock behind by 4 days. Checking timedatectl show, indicates

Timezone=America/Pacific
LocalRTC=no
CanNTP=yes
NTP=yes
NTPSynchronized=no

journalctl showed errors connecting to ntp.ubuntu.com.

Can subiquity check the status of timedatectl show, and if NTPSynchronized is not "yes" prompt user for NTP server? Not sure how feasible it is for subiquity to know if the time and date are correct without NTP or talking to some other server so I think allowing users to configure NTP with alternative servers is the best option here.

I've not recreated on VM, but I suspect that if you disable systemd-timesyncd, set the clock to something a few days back, then attempt and install it should recreate the apt update failure.