Email Notifier Service

email-notifier-service resolves email destinations and delivers notifications for the email channel. With app.sentinel, it also holds external watchdogs and sends a Down or Recovered alert by email.

HTTP serves POST /watchdogs/{name}/heartbeat. Without app.sentinel that route answers 404. Health in Compose stays the Kontiki registry live probe.

What it does

• Load email endpoints from YAML (app.endpoints).
• Expose the email channel catalog (RPC get_notification_channel_catalog).
• Consume email.alerting.notification.requested.
• Resolve destination using configured endpoint_key.
• Format alert notifications as multipart plain + HTML (same structured layout as Telegram: event_type banner, humanized attributes, Message when body adds info). Subject is the banner label.
• Send email through configured SMTP.
• When app.sentinel is set, accept watchdog heartbeats and send a structured Down or Recovered mail on the watchdog’s endpoint.
• Mark the instance degraded on repeated SMTP failures (@degraded_on); alert-delivery failures surface through Kontiki exception / alerting.

Stack

• Config: stack/notifiers/email.yaml (demo ships app.endpoints.inbox → MailHog)
• Local SMTP: MailHog (mailhog:1025, UI http://127.0.0.1:8025)
• Matching subscriptions: stack/subscription.yaml (core) or stack/subscription.demo.yaml (demo).

Message formatting

Alert notifications (context.kind = alert or a non-empty category) are rendered as multipart/alternative:

• Subject: humanized event_type (falls back to last category segment)
• text/plain: banner, attribute rows in producer insertion order, optional Message: when body differs from title, optional Details link
• text/html: same layout plus severity icon on the banner

Non-alert messages keep title as subject and title/body as content.

Shared parsing lives in boomerang.services.notifiers.common.structured_alert (also used by the Telegram notifier).

Event flow

Consumes:

• email.alerting.notification.requested

Behavior:

• parse payload as NotificationRequest,
• resolve address from configured endpoint,
• format plain + HTML body,
• send via SMTP (failures propagate as Kontiki exceptions).

External sentinel

Optional. POST /watchdogs/{name}/heartbeat with Authorization: Bearer <token> refreshes one watchdog. A matching token on a known name answers 204. A missing or wrong token answers 401. An unknown name, or no app.sentinel section, answers 404.

Down and Recovered are structured alerts (category kontiki.sentinel). The subject is Down (critical) or Recovered (low). The heartbeat name is the Watchdog attribute. They are sent through the endpoint named by endpoint_key. They do not go through the bus.

Keys and state machine: docs/configuration.md.