System Exists
backstage.system-exists
Verifies that the system referenced by spec.system in catalog-info.yaml
actually exists in the Backstage catalog (referential integrity). Reads
the collector's lookup result at .catalog.native.backstage.refs.system.
Fails when the declared system is absent from Backstage (collector
recorded exists=false). Passes when no system is declared (nothing to
cross-check — system-set owns "should it be set"). Skips (passes) when
referential integrity was not performed — i.e. the backstage collector
is not configured with backstage_url (no .refs.checked), or the lookup
errored transiently (.refs.system.error) — so an unconfigured collector
or a Backstage outage never turns this red.
Compatible Integrations
This guardrail works with the following integrations. Click to see how to use System Exists with each collector.
Enable This Guardrail
Add the parent policy to your lunar-config.yml to enable this guardrail.
policies:
- uses: github://earthly/lunar-lib/policies/backstage@v1.0.5
include: [system-exists]
# with: ...How This Guardrail Works
This guardrail is part of the Backstage Guardrails policy. It evaluates data collected by integrations and produces a pass/fail check with actionable feedback.
When enabled, this check runs automatically on every PR and in AI coding workflows, providing real-time enforcement of your engineering standards.
Learn How Lunar Works →Configuration Options
These inputs can be configured in your lunar-config.yml to customize
how the parent policy (and this guardrail) behaves.
| Input | Required | Default | Description |
|---|---|---|---|
required_annotations
|
Required | — | Annotation keys that must be present (and non-empty) in catalog-info.yaml `metadata.annotations`. Two forms are accepted. Comma-separated keys (presence-only, unchanged), e.g. `backstage.io/source-location,pagerduty.com/integration-key`. Or a YAML list, where each entry is either a bare key (presence-only) or a mapping with a `key` and optional value constraints: `type` (string|integer|number|boolean, default string), `min`/`max` (integer/number bounds), `min_length`/`max_length` (string length), `pattern` (full-match regex), and `enum` (allowed values). For example, a `key: example.com/service-tier` with `type: integer`, `min: 0`, `max: 5` requires that annotation to parse as an integer in 0–5. Annotation values are strings in Backstage, so `type` validates that the value *parses* as the declared type (`"2"` satisfies `integer`, `"2.5"` does not). `enum` inherits `type`: its entries are coerced to the declared type before comparison, so `type: integer` with `enum: [1,2,3]` compares integers while the default `type: string` compares strings. Constraints must match the declared type (`min`/`max` for integer/number; `min_length`/`max_length`/`pattern` for string). A value that violates a constraint fails the check; a malformed constraint (unknown type, min greater than max, invalid regex, a constraint on the wrong type, or an enum entry not of the declared type) makes it error. Empty (the default) disables the check. |
required_tag_patterns
|
Required | — | Comma-separated list of glob patterns; the component's `metadata.tags` must include at least one tag matching each pattern. Example: `location/*,runs-on/*`. Matching is case-insensitive. Empty (the default) disables the `required-tag-patterns` check. |
disallowed_annotations
|
Required | — | Comma-separated list of annotation keys that must NOT be present in catalog-info.yaml `metadata.annotations`. Example: `backstage.io/skip-checks`. Empty (the default) disables the `disallowed-annotations` check. |
disallowed_tag_patterns
|
Required | — | Comma-separated list of glob patterns; the component's `metadata.tags` must NOT include any tag matching these patterns. Example: `deprecated/*,internal-only`. Matching is case-insensitive. Empty (the default) disables the `disallowed-tag-patterns` check. |
Backstage Guardrails
This guardrail is part of the Backstage Guardrails policy, which includes 11 guardrails for repository and ownership.
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