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| 1 | +# Service Mesh Interface |
| 2 | + |
| 3 | +## Version |
| 4 | + |
| 5 | +This is SMI **spec** version **v0.5.0-WD**. |
| 6 | +Learn more about versioning [below](#versioning). |
| 7 | + |
| 8 | +## Table of Contents |
| 9 | + |
| 10 | +- [Abstract](#abstract) |
| 11 | +- [Objective](#objective) |
| 12 | +- [Technical Overview](#technical-overview) |
| 13 | +- [APIs](#apis) |
| 14 | + - [Traffic Access Control](#traffic-access-control) |
| 15 | + - [Traffic Split](#traffic-split) |
| 16 | + - [Traffic Specs](#traffic-specs) |
| 17 | + - [Traffic Metrics](#traffic-metrics) |
| 18 | +- [Appendix](#appendix) |
| 19 | + - [Terminology](#terminology) |
| 20 | + - [API Development Process](#api-development-process) |
| 21 | + - [Versioning](#versioning) |
| 22 | + |
| 23 | +## Abstract |
| 24 | + |
| 25 | +The Service Mesh Interface (SMI) is a specification for service meshes that run |
| 26 | +on Kubernetes. It defines a common standard that can be implemented by a variety |
| 27 | +of providers. This allows for both standardization for end-users and innovation |
| 28 | +by providers of Service Mesh Technology. SMI enables flexibility and |
| 29 | +interoperability, and covers the most common service mesh capabilities. |
| 30 | + |
| 31 | +## Objective |
| 32 | + |
| 33 | +### Goals |
| 34 | + |
| 35 | +The goal of the SMI API is to provide a common, portable set of Service Mesh |
| 36 | +APIs which a Kubernetes user can use in a provider agnostic manner. In this way |
| 37 | +people can define applications that use Service Mesh technology without tightly |
| 38 | +binding to any specific implementation. |
| 39 | + |
| 40 | +### Non-Goals |
| 41 | + |
| 42 | +It is a non-goal for the SMI project to implement a service mesh itself. It |
| 43 | +merely attempts to define the common specification. Likewise it is a non-goal to |
| 44 | +define the extent of what it means to be a Service Mesh, but rather a generally |
| 45 | +useful subset. If SMI providers want to add provider specific extensions and |
| 46 | +APIs beyond the SMI spec, they are welcome to do so. We expect that, over time, |
| 47 | +as more functionality becomes commonly accepted as part of what it means to be a |
| 48 | +Service Mesh, those definitions will migrate into the SMI specification. |
| 49 | + |
| 50 | +## Technical Overview |
| 51 | + |
| 52 | +The SMI is specified as a collection of Kubernetes APIs via Kubernetes Custom |
| 53 | +Resource Definitions (CRD) and Extension API Servers. These APIs can be |
| 54 | +installed onto any Kubernetes cluster and manipulated using standard tools. |
| 55 | +The APIs require an SMI provider to do something. |
| 56 | + |
| 57 | +To activate these APIs an SMI provider is run in the Kubernetes cluster. For the |
| 58 | +resources that enable configuration, the SMI provider reflects back on their |
| 59 | +contents and configures the provider's components within a cluster to implement |
| 60 | +the desired behavior. In the case of extension APIs, the SMI provider translates |
| 61 | +from internal types to those the API expects to return. |
| 62 | + |
| 63 | +This approach to pluggable interfaces is similar to other core Kubernetes APIs |
| 64 | +like [NetworkPolicy][1], [Ingress][2] and [CustomMetrics][3]. |
| 65 | + |
| 66 | +## APIs |
| 67 | + |
| 68 | +Find each API described at a high level below. Follow the links to see the |
| 69 | +individual API specification documents for the details. Each document outlines: |
| 70 | + |
| 71 | +- Specification |
| 72 | +- Possible use cases |
| 73 | +- Example implementations |
| 74 | +- Tradeoffs |
| 75 | + |
| 76 | +_Note: historical versions of the API specification as well as current working |
| 77 | +drafts can be found under the [apis/ directory](apis/)_ |
| 78 | + |
| 79 | +### Traffic Access Control |
| 80 | + |
| 81 | +Apply policies like identity and transport encryption across services. |
| 82 | + |
| 83 | +The [Traffic Access Control](apis/traffic-access/traffic-access-WD.md) API |
| 84 | +describes a resource to configure access to specific pods and routes based |
| 85 | +on the identity of a client for locking down applications to only allowed |
| 86 | +users and services. |
| 87 | + |
| 88 | +### Traffic Split |
| 89 | + |
| 90 | +Shift traffic between different services. |
| 91 | + |
| 92 | +The [Traffic Split](apis/traffic-split/traffic-split-WD.md) API describes |
| 93 | +a resource to incrementally direct percentages of traffic between various services |
| 94 | +to assist in building out canary rollouts. |
| 95 | + |
| 96 | +### Traffic Specs |
| 97 | + |
| 98 | +Describe traffic on a per-protocol basis. |
| 99 | + |
| 100 | +The [Traffic Specs](apis/traffic-specs/traffic-specs-WD.md) API describes |
| 101 | +a set of resources to define how traffic looks on a per-protocol basis. These |
| 102 | +resources work in concert with access control and other types of policy to manage |
| 103 | +traffic at a protocol level. |
| 104 | + |
| 105 | +### Traffic Metrics |
| 106 | + |
| 107 | +Capture key metrics like error rate and latency between services. |
| 108 | + |
| 109 | +The [Traffic Metrics](apis/traffic-metrics/traffic-metrics-WD.md) API |
| 110 | +exposes common traffic metrics for use by tools such as dashboards and autoscalers. |
| 111 | + |
| 112 | +## Appendix |
| 113 | + |
| 114 | +### Terminology |
| 115 | + |
| 116 | +- **SMI Provider**: An implementor of SMI. This could be a service mesh. |
| 117 | +- **API Group**: A set of resources that are exposed together. Each group may have |
| 118 | +one or more versions that evolve independently of other API Groups. Group names are |
| 119 | +in domain form. |
| 120 | + |
| 121 | +### API Development Process |
| 122 | + |
| 123 | +Please submit an issue or a pull request to this repository to propose a change. |
| 124 | +Changes are discussed on the [SMI community meetings](README.md/#communications). |
| 125 | +Changes should be made to working draft documents of each API which can be found |
| 126 | +in the corresponding directories under [apis/](apis/). Current working drafts |
| 127 | +documents have a suffix **-WD.md** |
| 128 | + |
| 129 | +### Versioning |
| 130 | + |
| 131 | +The spec has its own version listed [above](#version). This version describes the |
| 132 | +specification in its entirety. Although it is not related to the API specification |
| 133 | +versions, the minor version of the spec will be incremented every time any of the |
| 134 | +API Specification versions are incremented. |
| 135 | + |
| 136 | +[1]: https://kubernetes.io/docs/concepts/services-networking/network-policies/ |
| 137 | +[2]: https://kubernetes.io/docs/concepts/services-networking/ingress/ |
| 138 | +[3]: https://github.com/kubernetes/metrics#custom-metrics-api |
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