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Service Mesh Interface (SMI) was a Kubernetes-focused specification for expressing common service-mesh capabilities through provider-agnostic APIs. It is archived, not an actively maintained standard: CNCF moved it to Archived maturity on September 25, 2023, and its October 3 announcement pointed users toward Gateway API’s GAMMA initiative for service-mesh work.
What is Service Mesh Interface (SMI)?
SMI was a specification, not a service mesh product. Its goal was to give teams a common Kubernetes-oriented interface for capabilities that mesh implementations could support, including traffic policy, telemetry, and traffic management. It uses Kubernetes custom resources and extension mechanisms to describe those operations. CNCF’s SMI project page and the SMI specification repository describe that scope.
Provider-agnostic describes the design goal; it does not guarantee that every mesh implements every API or version, or behaves identically. Before relying on an SMI resource, check the documentation for the specific mesh, controller, and release running in your cluster.
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No. CNCF records that SMI was accepted on March 19, 2020, and moved to Archived maturity on September 25, 2023. CNCF announced the archival on October 3, 2023, explaining that no further work had happened under the SMI umbrella and that maintainers recommended following the GAMMA initiative under Kubernetes SIG Network. The SMI project site also labels the project archived.
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Chris Aniszczyk, CTO of CNCF, described the decision in the archival announcement: “In CNCF, projects have a lifecycle and sometimes that includes archiving a project, especially as sandbox projects are meant for experimentation.” Archival is a lifecycle status; it should not be confused with a claim that existing configurations immediately stop working. Whether they continue to work depends on the implementations and versions a cluster uses.
Which APIs did SMI define?
The archived repository lists the core specification as v0.6.0 and records these component versions. This is a historical inventory of the specification, not a statement about current implementation support.
| SMI component | Archived repository version | Purpose |
|---|---|---|
| Traffic Access Control | v1alpha3 | Describes access policy between service identities and traffic rules. |
| Traffic Metrics | v1alpha1 | Provides an API for traffic telemetry. |
| Traffic Specs | v1alpha4 | Describes traffic protocols and specifications used by other SMI APIs. |
| Traffic Split | v1alpha4 | Describes traffic distribution, including split-based routing. |
For exact resource fields and semantics, consult the relevant versioned documents in the SMI repository. A resource appearing in the specification does not mean a particular mesh or controller supports it.
How did SMI Traffic Access Control work?
In the Traffic Access Control specification, a TrafficTarget associates source identities, destination identities, and traffic rules. The specification describes access control as additive: matching permissions grant access, while traffic is denied by default. Its examples use Kubernetes service accounts as service identities and note that Kubernetes RBAC should control which pods can assume the destination service account. These are specification-level semantics; verify how the installed mesh implements them in the Traffic Access Control v1alpha3 document.
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What replaces SMI for Kubernetes service meshes?
CNCF’s archival announcement identified Gateway API’s GAMMA initiative as the direction maintainers recommended for consolidating service-mesh work. This is a direction to investigate, not proof of a one-to-one replacement or universal feature parity. Gateway API and the SMI APIs may not cover a team’s needs in the same way, and actual support depends on the target mesh, controller, and release.
Argo Rollouts documents its SMI integration through TrafficSplit resources and, after SMI’s archival, points users toward Gateway API, GAMMA, and the Argo Rollouts Gateway API plugin. That guidance applies to the integration described by Argo Rollouts; it does not establish a universal migration path for every SMI user. See its SMI traffic-management documentation.
How should a team plan a move from SMI?
- Inventory what is deployed. Find the SMI resources and API versions in use, such as
TrafficTargetorTrafficSplit, and identify the workloads and controllers that depend on them. - Map use cases, not just resource names. Record the behavior each configuration needs, including access policy, telemetry, or traffic distribution. Do not assume a Gateway API resource is an equivalent substitute based on its name alone.
- Check support in the target stack. Consult the documentation for the Gateway API implementation, mesh, controller, and release you plan to use. Confirm that the required use cases are supported there.
- Test the migration in your environment. Validate routing, access behavior, rollout handling, and any operational workflows affected by the change before relying on the new configuration.
For an SMI-based versus Gateway API-based approach, compare project maintenance status, coverage of your actual use cases, support in your target mesh and controller release, and migration effort and validation needs. The right path depends on those specifics, not on an assumption of automatic equivalence.
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