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MusterTemplateError

Meaning

A template failed to render. This alert has two sources with the same name, severity warning and this page:

  • The Internal alert, raised by Muster as an Alert of the built-in "Muster" Integration when a template of a Route or of a Destination starts failing, and resolved when that template renders again or, for a Route, when a new template of that kind is saved; for a Destination, also when the Destination is deleted. Its labels are route and route_name for a template of a Route — the Root message, the Alert line or the Ack timeout notice (template is root_message, line or ack_timeout_notice) — or destination and destination_name for a request template of an outgoing webhook (template is webhook_request).

  • The chart rule, on every failure counted in the last 15 minutes:

    sum by (route, destination, template) (increase(muster_template_errors_total{job="muster"}[15m])) > 0

    It fires at once (for: 0m) with the labels route, destination (one of them empty) and template. The counter also counts the URL templates of Link rules (template="link_rule"), which raise no Internal alert, so the chart rule can fire where the Internal alert does not.

Impact

  • A Route template that fails: the message is rendered with the Fallback template instead — every label under Muster's heading, with the footer and the buttons. People still see and act on the Alert Group, in a plainer format.
  • A request template of an outgoing webhook that fails: that request is not sent; the delivery or the Thread reply ends as Not delivered, with no fallback body.
  • A Link rule that fails: its link is left out of the Alert Group's links.
  • Everything else keeps working.

Diagnosis

  1. Open System status (/admin/system-status): Template errors lists every Route and Destination whose template fails, with the kind — Root message, Alert line, Ack timeout notice, Link rule or Request template.
  2. Open the Route page (/routes/<id>): the banner says "Template error since HH:MM: {error}." with the line and column that failed. The Route list marks the Route with "Template error".
  3. Read the log lines:
    • fallback_template_used (route, group, template, error): a Route template failed and the message used the Fallback template.
    • webhook_template_failed (destination, group, request, error): a request template of an outgoing webhook failed.
    • link_rule_failed (link_rule, route, group, error): the URL template of a Link rule failed.
  4. Check which labels the template reads: a template that works for most Alert Groups often fails on one whose Alerts lack a label or carry an unexpected value.

Fix

  • Correct the template so that it handles the missing or unexpected value, and check it with the preview before you save it. For outgoing webhooks, see Template errors.
  • For a Link rule, correct its URL template under Organization → Link rules (/admin/organization/link-rules).
  • The Internal alert resolves when the next message of the Route renders with the template (logged as template_recovered) or when a new template of that kind is saved on the Route, and when the next request of the Destination renders or the Destination is deleted. Deleting a Route does not resolve it. The chart rule resolves 15 minutes after the last failure.