Single bookworm-slim image running opendkim + panel + postfix under
supervisord with enforced start ordering (spec 4):
- build/Dockerfile: multi-stage static Go build; runtime installs postfix,
opendkim, cyrus-sasl, supervisor, logrotate; unprivileged panel user (7.6.8).
- build/supervisord.conf: priority ordering opendkim -> panel -> postfix;
crashexit event listener terminates the container on any FATAL process.
- build/postfix-wrapper.sh: waits for both milter sockets (test -S, 30s
timeout) before `postfix start-fg`, exits non-zero on timeout.
- panel: HTTP :8080 stub + /healthz, journal-milter socket stub (so the
wrapper's readiness probe passes), log-tailer stub; SIGTERM graceful stop.
Verified on the dev server: image builds, three processes live, panel serves
the stub, wrapper waits for sockets, and an unrecoverable panel failure brings
the container down cleanly.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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