Change:
<del> --- reviewers: - johnbelamaric - imroc title: Topology-aware traffic routing with topology keys content_type: concept weight: 150 --- <!-- overview --> {{< feature-state for_k8s_version="v1.21" state="deprecated" >}} {{< note >}} This feature, specifically the alpha `topologyKeys` API, is deprecated since Kubernetes v1.21. [Topology Aware Routing](/docs/concepts/services-networking/topology-aware-routing/), introduced in Kubernetes v1.21, provides similar functionality. {{</ note >}} _Service Topology_ enables a service to route traffic based upon the Node topology of the cluster. For example, a service can specify that traffic be preferentially routed to endpoints that are on the same Node as the client, or in the same availability zone. <!-- body --> ## Topology-aware traffic routing By default, traffic sent to a `ClusterIP` or `NodePort` Service may be routed to any backend address for the Service. Kubernetes 1.7 made it possible to route "external" traffic to the Pods running on the same Node that received the traffic. For `ClusterIP` Services, the equivalent same-node preference for routing wasn't possible; nor could you configure your cluster to favor routing to endpoints within the same zone. By setting `topologyKeys` on a Service, you're able to define a policy for routing traffic based upon the Node labels for the originating and destination Nodes. The label matching between the source and destination lets you, as a cluster operator, designate sets of Nodes that are "closer" and "farther" from one another. You can define labels to represent whatever metric makes sense for your own requirements. In public clouds, for example, you might prefer to keep network traffic within the same zone, because interzonal traffic has a cost associated with it (and intrazonal traffic typically does not). Other common needs include being able to route traffic to a local Pod managed by a DaemonSet, or directing traffic to Nodes connected to the same top-of-rack switch for the lowest latency. ## Using Service Topology If your cluster has the `ServiceTopology` [feature gate](/docs/reference/command-line-tools-reference/feature-gates/) enabled, you can control Service traffic routing by specifying the `topologyKeys` field on the Service spec. This field is a preference-order list of Node labels which will be used to sort endpoints when accessing this Service. Traffic will be directed to a Node whose value for the first label matches the originating Node's value for that label. If there is no backend for the Service on a matching Node, then the second label will be considered, and so forth, until no labels remain. If no match is found, the traffic will be rejected, as if there were no backends for the Service at all. That is, endpoints are chosen based on the first topology key with available backends. If this field is specified and all entries have no backends that match the topology of the client, the service has no backends for that client and connections should fail. The special value `"*"` may be used to mean "any topology". This catch-all value, if used, only makes sense as the last value in the list. If `topologyKeys` is not specified or empty, no topology constraints will be applied. Consider a cluster with Nodes that are labeled with their hostname, zone name, and region name. Then you can set the `topologyKeys` values of a service to direct traffic as follows. * Only to endpoints on the same node, failing if no endpoint exists on the node: `["kubernetes.io/hostname"]`. * Preferentially to endpoints on the same node, falling back to endpoints in the same zone, followed by the same region, and failing otherwise: `["kubernetes.io/hostname", "topology.kubernetes.io/zone", "topology.kubernetes.io/region"]`. This may be useful, for example, in cases where data locality is critical. * Preferentially to the same zone, but fallback on any available endpoint if none are available within this zone: `["topology.kubernetes.io/zone", "*"]`. ## Constraints * Service topology is not compatible with `externalTrafficPolicy=Local`, and therefore a Service cannot use both of these features. It is possible to use both features in the same cluster on different Services, only not on the same Service. * Valid topology keys are currently limited to `kubernetes.io/hostname`, `topology.kubernetes.io/zone`, and `topology.kubernetes.io/region`, but will be generalized to other node labels in the future. * Topology keys must be valid label keys and at most 16 keys may be specified. * The catch-all value, `"*"`, must be the last value in the topology keys, if it is used. ## Examples The following are common examples of using the Service Topology feature. ### Only Node Local Endpoints A Service that only routes to node local endpoints. If no endpoints exist on the node, traffic is dropped: ```yaml apiVersion: v1 kind: Service metadata: name: my-service spec: selector: app: my-app ports: - protocol: TCP port: 80 targetPort: 9376 topologyKeys: - "kubernetes.io/hostname" ``` ### Prefer Node Local Endpoints A Service that prefers node local Endpoints but falls back to cluster wide endpoints if node local endpoints do not exist: ```yaml apiVersion: v1 kind: Service metadata: name: my-service spec: selector: app: my-app ports: - protocol: TCP port: 80 targetPort: 9376 topologyKeys: - "kubernetes.io/hostname" - "*" ``` ### Only Zonal or Regional Endpoints A Service that prefers zonal then regional endpoints. If no endpoints exist in either, traffic is dropped. ```yaml apiVersion: v1 kind: Service metadata: name: my-service spec: selector: app: my-app ports: - protocol: TCP port: 80 targetPort: 9376 topologyKeys: - "topology.kubernetes.io/zone" - "topology.kubernetes.io/region" ``` ### Prefer Node Local, Zonal, then Regional Endpoints A Service that prefers node local, zonal, then regional endpoints but falls back to cluster wide endpoints. ```yaml apiVersion: v1 kind: Service metadata: name: my-service spec: selector: app: my-app ports: - protocol: TCP port: 80 targetPort: 9376 topologyKeys: - "kubernetes.io/hostname" - "topology.kubernetes.io/zone" - "topology.kubernetes.io/region" - "*" ``` ## {{% heading "whatsnext" %}} * Read about [Topology Aware Hints](/docs/concepts/services-networking/topology-aware-hints/) * Read [Connecting Applications with Services](/docs/tutorials/services/connect-applications-service/) </del>

Discussion:
This is a Bug Report <!-- Thanks for filing an issue! Before submitting, please fill in the following information. --<!-- See for guidance on writing an actionable issue description. --<!--Required Information--Problem: Topology-aware traffic routing with topology keys is deprecated since 1.21 Confirm if it's removed and remove the related documentation if feature is removed Proposed Solution: Remove Service Topology page Page to Update: <!--Optional Information (remove the comment tags around information you would like to include)--<!--Kubernetes Version:--Deprecated since 1.21 <!--Additional Information:--
/kind cleanup /language en
I can look into this. /assign
/sign network /triage accepted /priority important-longterm
Thanks