docs(prometheus-api-bridge): add guide for using SigNoz as a Prometheus data source

[simonepri]

📄 Summary

SigNoz docs have no answer for the read side of a Prometheus migration. The Prometheus & Grafana migration guide gets metrics in and stops there, but the tools people were running Prometheus for still expect a Prometheus URL to query: KEDA, HPA, VPA, Headlamp, Ray, OpenCost, Argo Rollouts, Grafana. In practice teams finish the migration and then keep a Prometheus server alive purely to serve those reads.

This adds a page covering that gap, using Prometheus API Bridge, an open source service I wrote and maintain. It follows the same pattern as the existing Kubernetes HPA with SigNoz Metrics tutorial: a third-party tool, documented with a disclaimer that it is not a SigNoz product.

The page is deliberately thin on reference material. There is no per-tool table and no endpoint list, because both would go stale here as the project changes. It links upstream for those and keeps only what a reader needs to get from zero to a working setup.

File	Change
data/docs/metrics-management/prometheus-api-bridge.mdx	The new guide
data/docs-side-nav/main.json	Sidebar entry under Metrics > User Guides
data-assets/img/docs/prometheus-api-bridge-arch.svg	Architecture diagram used by the guide
data/docs/migration/migrate-from-grafana/metrics.mdx	Adds a callout linking to the guide, placed before ## Validate

Issues closed by this PR

N/A

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✅ Change Type

• ✨ Feature

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🧪 Testing Strategy

• yarn check:docs-metadata, yarn check:doc-redirects, yarn test:docs-metadata, yarn test:doc-redirects all pass, and yarn build is clean.
• Rendered locally with yarn start to check the page, the sidebar entry, and the migration callout. This PR comes from a fork, so there is no preview deployment to link.
• All internal and external links verified to return 200.
• Claims were checked against the bridge's source and its end-to-end fixtures rather than its README. That corrected several details, including which endpoints SigNoz actually serves and the fact that the Headlamp Prometheus plugin has no URL field to set.

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👀 Notes for Reviewers

• Disclosure. I am the author of the bridge. The page carries the same "not an official SigNoz product" admonition as the HPA adapter tutorial, so please flag anything that reads as promotional.
• Placement. Metrics > User Guides, beside Kubernetes HPA with SigNoz Metrics, which is the existing precedent for a third-party integration. I did not add it to the Integrations listicle, since that section is about getting telemetry into SigNoz and this is query-side. Happy to move it if you would rather it live there.
• Diagram is SVG, not WebP, matching the existing k8s-hpa-signoz-adapter-arch.svg in canvas size and visual language. Happy to convert if you prefer WebP for consistency.
• No frontend files are touched, so no @SigNoz/frontend review should be required.

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1 Skipped Deployment

Project	Deployment	Actions	Updated (UTC)
signoz-web	Ignored	Preview	Aug 30, 2026 9:04pm