generated serial is too long

[Christian Garbs]

nsd from Debian Buster does a proper check of the serial number and errors out, because the currently generated YYYYMMDDhhmmss is much more than a 32 bit unsigned integer:

current value:   20190723001745
maximum allowed:     4294967295

We need to shorten our pattern. We also need to keep the 1 second resolution to avoid duplicate serial numbers.

Possible fixes:

• use unix timestamp
  • pro: signed 32bit integer, so it fits even after the rollover in 2038
  • con: not readable by a mere human
• skip the year
  • pro: easy to parse by a human
  • pro: this script is thought to be called multiple times per day, so the year is not really relevant
  • cons: none yet (?)
• use an abstract atomic counter instead of a timestamp-derived number
  • pro: sub-second resolution, no need for the sleep 1 hack to ensure unique timestamps
  • con: time of last update not contained in DNS information
  • con: hard to implement (concurrent access to simple text file)

Looks like "skip the year" to me.