[Gerrrt]

What changed

A custom ntfy template, stacks/sensitive/ntfy/templates/homelab.yml, mounted at ntfy's default template-dir. Alertmanager payloads render like this, measured on the pinned image:

P5 | 🔴 ntfy is not reachable at https://ntfy.matrix.elysium/v1/health
Probed by dns and got no successful response for five minutes.
📍 trinity

P2 | ✅ Resolved: UPS is on battery
Mains lost at the rack.
📍 mjolnir

P3 | 🟠 3 × SnmpTargetUnreachable
• SNMP target pfsense unreachable
• SNMP target ups unreachable
• SNMP target ilo unreachable

Priority follows severity:

• Critical is 5: Android's loud channel, and time-sensitive on iOS.
• Warning is 3.
• Resolved alerts and the daily Watchdog are 2.

Why

Every rule's description is a paragraph written for a keyboard, and the phones received it whole. The ntfy.sh copies received the raw webhook JSON.

Blast radius

• trinity: one new read-only directory mount into sensitive-ntfy. make up STACK=sensitive recreates the container.

• prometheus: secrets edit needed. Nothing changes on the phones until it's done.

  • The three in-house ALERTMANAGER_*_WEBHOOK_URL values change ?template=alertmanager to ?template=homelab.
  • The two *_EXTERNAL_URL values gain ?template=alertmanager. ntfy.sh can't load our template, and the built-in beats raw JSON.
  • url_file is read at notify time, so this takes effect on the next notification with no restart.

• If the template ever fails to render, ntfy rejects that publish. AlertmanagerNotificationsFailing then fires through the ntfy.sh copy.

• No change to network segmentation or firewall rules

• No new port published to a VLAN that could not already reach the service

• No credential added outside secrets/*.sops.yaml

Verification

• Payload shapes: six rendered through ntfy:v2.28.0 with the template mounted read-only and all capabilities dropped: critical, warning, resolved, a group of three, Watchdog, and one with no annotations. The output is above.

• Real rules: the first-sentence rule was checked against all 102 alerting rules' descriptions. Four run past 200 characters and are trimmed with an ellipsis. Those with no description show severity · category instead of ntfy's filler text, "triggered".

• Checks: make validate passes, and yamllint is clean.

• make validate passes

• Deployed to the lab and confirmed working: after merge, make up STACK=sensitive on trinity and the URL edit on prometheus, then step 8's synthetic page shows it on the phones

• Docs updated: stack README, secrets template, alertmanager.yaml comment, runbook

Refs #136

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