selfpost/docs/architecture.md

SelfPost — architecture (as-built)

Source of truth: the code tree, not historical specs. Synchronise this file when env keys, routes, or mail-path behaviour change. Verification method: documentation-plan.md §2.

User install/operations: README.md. Product boundaries: product.md.

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Image and processes

Single Debian slim image. entrypoint.sh (root) fixes /data ownership and milter socket directories, requires SELFPOST_HOSTNAME (FQDN with at least one dot; no scheme, port, or spaces — invalid or empty value → exit 1 before Postfix config or supervisord), then execs supervisord as PID 1.

The hostname is not a tunable default: it must match PTR/rDNS, TLS CN/SAN, and SASL realm together. Soft fallbacks (localhost in the panel vs container ID in Postfix) split realms and break SMTP AUTH with a silent 535 in clients while the panel looks healthy. Shipped docker-compose.yml already requires the variable; the entrypoint gate catches docker run, custom compose, and k8s.

Managed programs (build/supervisord.conf):

Program	User	Priority	Role
opendkim	opendkim	100	DKIM signing milter
panel	panel	200	HTTP UI + journal-milter + log-tailer goroutine
postfix	root (wrapper)	300	MTA — started only after both milter sockets exist
postfix-reload	root	—	On-demand postfix reload (autostart off)
cert-reload	root	400	Daily postfix reload for renewed TLS certs
logrotate	root	400	Periodic mail.log rotation

Start order: OpenDKIM → panel (opens journal-milter socket) → Postfix wrapper polls unix sockets (timeout MILTER_WAIT_TIMEOUT, default 30s) then postfix start-fg.

crashexit event listener exits the container on any managed process FATAL so Docker restart: unless-stopped recreates a broken instance.

Liveness: GET /healthz (unauthenticated) returns 200 when opendkim, panel, and postfix are RUNNING; Docker HEALTHCHECK uses the same probe.

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Mail path

Client ──TLS+SASL──► Postfix (465 smtps, optional 587 submission)
                         │
                         ├─► OpenDKIM milter (sign, tempfail on failure)
                         ├─► journal-milter (send log + L2 rate limits, fail-open)
                         └─► outbound MX delivery (port 25 client)

Postfix (build/postfix-config.sh)

• 465/smtps — implicit TLS, SASL required; primary listener.
• 587/submission — only when SUBMISSION_ENABLE=true; STARTTLS with smtpd_tls_security_level=encrypt.
• No open relay — permit_sasl_authenticated, reject_unauth_destination; smtpd_sender_login_maps + reject_sender_login_mismatch.
• Level-1 rate limit — smtpd_client_message_rate_limit / anvil_rate_time_unit from RATE_LIMIT_* env vars; independent of milter.
• Chroot disabled for all services (DNS/TLS inside container).
• TLS certs — read-only mount at TLS_CERT_FILE / TLS_KEY_FILE; daily reload via cert-reload.

OpenDKIM

Per-domain keys under /data/opendkim/keys; KeyTable / SigningTable maintained by the panel. Socket /run/opendkim/opendkim.sock.

Panel binary (cmd/panel)

One process, three roles:

1. HTTP server — :8080 (PANEL_HTTP_ADDR); HTTPS terminated by reverse proxy only.
2. journal-milter — unix socket JOURNAL_MILTER_SOCKET; records From/To/ Subject/SASL user at DATA; enforces level-2 rate limits; fail-open (default_action=accept) so milter failure does not stop mail.
3. log-tailer — follows MAIL_LOG, updates send-log delivery status by queue-id. Send-log queued → sent transitions depend on this goroutine alone (UpdateStatus is only called from internal/logtail).

Milter chain in Postfix: OpenDKIM (tempfail) then journal (accept on failure).

Log tailer and mail.log rotation

mail.log lives under /var/log (not in /data). Rotation uses rename + postfix reload (build/logrotate-mail.conf), not copytruncate — the latter can drop status=sent lines and leave send-log rows stuck at queued. After rename, logrotate runs create 0644 root root (Postfix recreates the file lazily on first write as mode 0600, which the unprivileged panel user cannot read). follow() drains the old inode once more before switching descriptors; the panel treats a missing log file as an empty tail, not an error.

Known gaps (same class of loss, not fixed by rename rotation):

• Panel restart — follow() starts at end-of-file; lines written while the panel was down are never parsed; in-flight send-log rows may stay queued.
• Container recreate — /var/log is ephemeral; the log is lost with the container.

Possible follow-ups if these become painful: persist read offset across restarts, mount mail log under /data, or reconcile stuck rows via postqueue.

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Panel HTTP surface

Route table: internal/web/web.go. Authenticated unless noted.

Route	Purpose
/healthz	Liveness (no auth)
/setup/*	One-time admin bootstrap
/login, /logout	Session auth
/status	Process, cert, socket, PTR checks
/domains, /domains/*	Domain and application CRUD, DKIM, L2 limits
/deliveries	Send log with filters
/mail-queue	Postfix queue view
/system-log	mail.log tail
/reload	Reload OpenDKIM + Postfix maps
/backup	Full backup download, domain import
/account	Admin username/password

HTMX polling refreshes monitoring fragments; polling does not extend session idle timeout (only non-HX-Request GET and mutating requests count as activity).

Sessions

Stored in SQLite (sessions table, migration 0002): cookie holds a random token; the database stores SHA-256 of the token, not the token itself — a stolen DB or backup archive does not alone grant login, but a browser that still holds the cookie works after process restart, redeploy, or full backup restore.

• Idle timeout — sliding window, PANEL_SESSION_IDLE_DAYS (default 7); no absolute cap (regular use keeps the session alive indefinitely).
• Renewal — DB last_seen and cookie Max-Age update at most once per hour (renewThreshold in internal/web/session.go).
• Password change — all other sessions are deleted; the current session stays active (internal/store/sessions.go, handlers_account.go).

Restoring an older backup also restores session rows: a session invalidated after that backup was taken can become valid again if the browser still has the cookie and idle timeout has not expired.

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Persistence (/data bind mount)

Path	Contents
selfpost.db	SQLite: domains, apps, admin, sessions, send log, L2 limits
setup-token	First-run setup token file
opendkim/	DKIM keys + tables
sasl/sasldb2	Application SASL credentials
postfix/sender_login_maps	Login → From binding
manifest.json	Backup version stamp (consumed on restore)

Not in /data: TLS certificates (reverse-proxy mount), Postfix queue (transit mail not migrated by design).

Rotation: send-log retention SEND_LOG_RETENTION_DAYS (default 90); mail.log via logrotate (14 rotated files, check every 6h, rename + postfix reload in postrotate — see § Log tailer above).

Backup: panel button or selfpost-backup CLI — SQLite snapshot + tar of /data tree; version check on restore. Stopped-container tar of ./data is safe (see README).

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Security (summary)

Mandatory checklist: security.md. Accepted trade-offs (CSRF origin check, no CSRF tokens) are documented there separately.

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Configuration

Public and internal env vars: README § Environment variables. Regression test: cmd/panel/envdoc_test.go.