Minor On a system configured to use DNS input adapters a 'ods-signer clear' command was issued for a zone. Just after that the zone signing started failing with the error message:
[worker[3]] sign zone my_zone
[zone] unable to update zone my_zone soa serial: failed to find soa rrset
[worker[3]] unable to sign zone my_zone: failed to increment serial
[worker[3]] CRITICAL: failed to sign zone my_zone: General error
[worker[3]] backoff task [sign] for zone my_zone with 960 seconds
The solution was to stop the signer, remove the my_zone.xfrd* files from the /var/opendnssec/tmp/ directory and start the signer again.
The suspicion is that there is a race condition that can cause this problem with the signer.