proposal: Prometheus internal telemetry as an OTel semantic convention registry - #86
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I would like to assess what alternatives we have that could be built-in e.g. client_golang and would be lighter. And I would also want to better understand the scope of this: |
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…n registry Define every metric the Prometheus binary exposes in a single OTel semantic convention registry, and use it as the source of truth for instrumentation code, documentation, and contract testing. Instrumentation code and per-package documentation are generated from the registry with Weaver, so neither can drift from the schema. Weaver is confined to build-time authoring. Contract testing runs without a Collector or a Weaver binary. `promtool check metrics --schema` validates a running Prometheus from outside and works for any exporter in any language. An in-process check over `Collector.Describe()` also covers metrics that never produce a sample, which telemetry-based validation cannot see. Both need a small, dependency-free addition to client_golang, since `prometheus.Desc` exposes no structural accessors today. Stability levels are recorded as schema information so lifecycle can be expressed and changes to it reviewed. Defining what `stable` obligates, how long a deprecation cycle runs, and which existing metrics are stable is left to a follow-on proposal. A consumable registry also lets downstream projects detect drift themselves. awesome-prometheus-alerts hardcodes 37 distinct prometheus_* metric names and perses/community-mixins writes them into dashboard queries, with no way to validate either against a release. Publishing a versioned schema of renames between releases stays a follow-on.
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@roidelapluie thanks for comment, I've updated a few things in the doc aiming to cover what you raised, let me know your thoughts |
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Had some minutes in the airport to review this, it's not a complete review though 😅
| * [Required] Define Prometheus' internal telemetry as a formal OTel semantic convention registry (a single `registry.yaml`), making it the single machine-readable source of truth for every metric Prometheus exposes. | ||
| * [Required] Generate instrumentation code from the registry, eliminating hand-written metric definitions in Go. | ||
| * [Required] Generate metric documentation from the registry that cannot drift from the implementation. | ||
| * [Nice to have] Enable contract testing through `promtool`: validate that a running Prometheus exposes exactly what the registry says, with no OTel Collector and no Weaver binary in the test path. |
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why not use the tools that already exist for this? 🙃
| The primary surface is `promtool`. It already reads text exposition from stdin, already runs `promlint` over it, and already exits 3 when it finds problems: | ||
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| ``` | ||
| curl -s http://localhost:9090/metrics | promtool check metrics --schema registry.yaml |
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By default, Prometheus does not emit all metrics it is instrumented with. For example, if Remote Write isn't configured for an instance, it won't expose any Remote Write metrics.
What would happen in that situation, should check metrics fail because the metric exists in the schema but not in the /metrics endpoint?
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It also exposes other metrics that aren't Prometheus related, like go and http metrics, what happens in these situations?
Address review feedback that the goals stated the solution rather than what it buys. The goals now describe the outcome (one machine-readable description, no hand-written descriptors, docs that cannot drift), and OTel semantic conventions appear as the mechanism in the How section. Also replace the OTel-alignment bullet in Why with the concrete problem underneath it: nothing can describe what a Prometheus emits without scraping a live instance. Signed-off-by: Nicolas Takashi <nicolas.takashi@dash0.com>
Address review feedback on the promtool path. Contract testing is now a single mechanism: a Go test that reads Collector.Describe() and compares the declared metrics to the registry. Drop promtool --schema. It could not verify that every declared metric is present, because text exposition only contains metrics that produced a sample, and it would have failed on metrics Prometheus does not own. The Describe() path sees the full declared surface either way. Add Weaver live-check as an explicit alternative so the reasons for not using the existing tool sit in Alternatives rather than buried in the contract testing section. Remove promlint from the design; it stays only in the alternative that exists to reject it. Signed-off-by: Nicolas Takashi <nicolas.takashi@dash0.com>
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This proposal defines all metrics exported by the Prometheus binary as a formal OTel semantic convention registry. Making the schema machine-readable enables auto-generated instrumentation code, always-in-sync documentation, contract testing against live instances, and a lifecycle model for safe metric evolution across the Prometheus ecosystem.
Proof-of-concept implementation: prometheus/prometheus#17868