Guardrails on shared data planes
Enterprise Tier
A data plane is shared capacity: it can host gateways for many projects at once, and each of those projects can carry its own guardrails. This page explains how guardrail enforcement works on that shared capacity — how enforcement is scoped to each project, how gateway attachment determines which guardrails a data plane enforces, and which signals to wire into alerting.
Persona: Platform operator or security stakeholder running data planes that serve more than one project.
What you will learn
- Each project's guardrails apply only to that project's traffic.
- Gateway attachment health is enforcement health: while a project's gateway attachment is failed, that project's guardrails are not enforced.
- Requests without project identity are blocked on a guardrail-carrying data plane, and the data plane counts them in metrics you should alert on.
Each project's guardrails apply only to that project's traffic
Guardrails are project policies: a guardrail authored under one project belongs to that project alone. Every gateway serves exactly one project, and the platform stamps each request with the project it belongs to before guardrails are evaluated, so the gateway evaluates only the guardrails owned by the request's project. A project that has configured no guardrails is unaffected by the policies of the other projects sharing the data plane.
Selection is per request. All served projects' guardrails coexist on the same data plane; on each request, the gateway selects the policy set that belongs to the project identity stamped on that request.
Gateway attachment health decides what is enforced
The set of projects whose guardrails a data plane enforces is derived from the project gateways attached to it — provisioning a gateway for a project on a data plane is what enrols that project's guardrails there.
That makes gateway attachment health part of enforcement health. While a project's gateway attachment is in a failed state, none of that project's guardrails are enforced on that data plane; enforcement resumes when the attachment is repaired. Traffic that cannot be attributed to a served project is blocked (see the identity section below).
When a gateway attachment fails:
- Review the per-gateway health indicators on the data plane, following Manage multiple gateways on a data plane.
- Repair or re-provision the failed attachment to restore enforcement for that project.
Alert on requests missing project identity
The platform stamps identity onto every request as it crosses the gateway — the same identity surfaced on telemetry as the x-tars-customer and x-router-project-id header-mapped attributes in the OpenTelemetry reference. Applications do not set these; the data plane does, and guardrail selection depends on them.
On a data plane with any guardrails configured, a request that reaches guardrail evaluation without this identity is blocked, with no guardrail evaluated: an unattributable request cannot be matched to its project's policy. On a data plane with no guardrails configured at all, such requests are allowed, since there is nothing to enforce.
In both cases the data plane emits metrics counting requests that arrive without identity. These counters are the canary for a misconfigured or degraded request path, and they deserve a standing alert:
- Wire an alert on the missing-identity counters in the metrics stream each data plane exposes (see OpenTelemetry traces and metrics for the delivery paths). Under normal operation the rate is zero.
- Treat a sustained non-zero rate as an incident. On a guardrail-carrying data plane it means live traffic is being blocked; on a guardrail-free data plane it means requests are flowing without project attribution. Either way the request path needs repair, starting with the health of the data plane's gateways.
Where to go next
About guardrails
The policy model: guardrails, rules, providers, patterns, and how a rule is evaluated.
Manage multiple gateways on a data plane
Review the gateways a data plane manages, their owning projects, and their health.
Guardrails best practices & FAQ
Roll out, tune, and operate guardrails in production without self-inflicted outages.
OpenTelemetry traces and metrics
The metric families and identity attributes the data plane exposes for alerting.