feat(secondary): add fallthrough support#8041
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Allow the secondary plugin to pass NXDOMAIN queries to the next plugin in the chain, enabling split DNS setups where a transferred zone contains only partial records. The file.File ServeDNS method already checks Fall.Through on NXDOMAIN, but secondaryParse never exposed the directive. This adds parsing for 'fallthrough [ZONES...]' following the same pattern used by file, hosts, and kubernetes plugins. Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>
yongtang
approved these changes
May 20, 2026
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1. Why is this pull request needed and what does it do?
Allow the secondary plugin to pass NXDOMAIN queries to the next plugin in the chain, enabling split DNS setups where a transferred zone contains only partial records.
The
file.FileServeDNS method already checksFall.Throughon NXDOMAIN, butsecondaryParsenever exposed the directive. This adds parsing forfallthrough [ZONES...]following the same pattern used by file, hosts, and kubernetes plugins.Example:
Records in the transferred zone are served authoritatively and NXDOMAIN queries fall through to the forward plugin.
2. Which issues (if any) are related?
Fixes #8017
3. Which documentation changes (if any) need to be made?
Includes plugin documentation update for the
secondaryplugin.4. Does this introduce a backward incompatible change or deprecation?
No, this is opt-in. Without the
fallthroughdirective, thefall.Fzero value meansThrough()always returns false. Existing configurations are unaffected.