0010. Hot reload by polling and SIGHUP, blocking settings only

• Status: Accepted; amended by 0016 ([local] also applies live)
• Date: 2026-10-16

Context

Rules must change without restarting dns-rs, including in containers where the configuration is a mounted Kubernetes ConfigMap. Sockets, the upstream client and the cache are created at startup. See also 0007, which planned keeping the last valid version of a list across refreshes.

Decision

• The configuration file is read every 10 seconds and compared by content, so a ConfigMap swap counts as an edit. SIGHUP triggers an immediate reload; signals arriving while a reload is pending merge into it.
• Only [blocking] changes apply live. server.listen, upstream.server, upstream.timeout and cache.size are reported once as needing a restart and are not applied.
• An invalid or missing file is rejected, logged once, and the previous configuration stays in force.
• All lists are downloaded again every blocking.refresh (default 24h, minimum 1m, so providers do not see every replica download every few seconds). A list that fails keeps its last valid version. A configuration reload downloads only lists that are new; removed lists stop blocking.
• Lists are parsed and the policy is compiled on a blocking thread, and lists are shared through Arc, so building a policy copies no rules and does not delay queries.

Consequences

• A change takes up to 10 seconds to apply unless SIGHUP is sent.
• Changing the listen address, upstream or cache size still requires a restart.
• Each replica downloads lists independently; a shared source is not implemented.