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Merge pull request #39499 from sftim/20230216_service_update_part_14 

Revise Service concept, part 14
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Kubernetes Prow Robot 2023-02-21 08:25:57 -08:00 committed by GitHub
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@ -71,14 +71,15 @@ balancer in between your application and the backend Pods.
## Defining a Service ## Defining a Service
A Service in Kubernetes is a REST object, similar to a Pod. Like all of the A Service in Kubernetes is an
REST objects, you can `POST` a Service definition to the API server to create {{< glossary_tooltip text="object" term_id="object" >}}
a new instance. (the same way that a Pod or a ConfigMap is an object). You can create,
The name of a Service object must be a valid view or modify Service definitions using the Kubernetes API. Usually
[RFC 1035 label name](/docs/concepts/overview/working-with-objects/names#rfc-1035-label-names). you use a tool such as `kubectl` to make those API calls for you.
For example, suppose you have a set of Pods where each listens on TCP port 9376 For example, suppose you have a set of Pods that each listen on TCP port 9376
and contains a label `app.kubernetes.io/name=MyApp`: and are labelled as `app.kubernetes.io/name=MyApp`. You can define a Service to
publish that TCP listener:
```yaml ```yaml
apiVersion: v1 apiVersion: v1
@ -94,16 +95,20 @@ spec:
targetPort: 9376 targetPort: 9376
``` ```
This specification creates a new Service object named "my-service", which Applying this manifest creates a new Service named "my-service", which
targets TCP port 9376 on any Pod with the `app.kubernetes.io/name=MyApp` label. targets TCP port 9376 on any Pod with the `app.kubernetes.io/name: MyApp` label.
Kubernetes assigns this Service an IP address (sometimes called the "cluster IP"), Kubernetes assigns this Service an IP address (the _cluster IP_),
which is used by the Service proxies that is used by the virtual IP address mechanism. For more details on that mechanism,
(see [Virtual IP addressing mechanism](#virtual-ip-addressing-mechanism) below). read [Virtual IPs and Service Proxies](/docs/reference/networking/virtual-ips/).
The controller for that Service continuously scans for Pods that
match its selector, and then makes any necessary updates to the set of
EndpointSlices for the Service.
The name of a Service object must be a valid
[RFC 1035 label name](/docs/concepts/overview/working-with-objects/names#rfc-1035-label-names).
The controller for the Service selector continuously scans for Pods that
match its selector, and then POSTs any updates to an Endpoint object
also named "my-service".
{{< note >}} {{< note >}}
A Service can map _any_ incoming `port` to a `targetPort`. By default and A Service can map _any_ incoming `port` to a `targetPort`. By default and
@ -177,8 +182,8 @@ For example:
* You are migrating a workload to Kubernetes. While evaluating the approach, * You are migrating a workload to Kubernetes. While evaluating the approach,
you run only a portion of your backends in Kubernetes. you run only a portion of your backends in Kubernetes.
In any of these scenarios you can define a Service _without_ a Pod selector. In any of these scenarios you can define a Service _without_ specifying a
For example: selector to match Pods. For example:
```yaml ```yaml
apiVersion: v1 apiVersion: v1
@ -262,9 +267,9 @@ selector will fail due to this constraint. This prevents the Kubernetes API serv
from being used as a proxy to endpoints the caller may not be authorized to access. from being used as a proxy to endpoints the caller may not be authorized to access.
{{< /note >}} {{< /note >}}
An ExternalName Service is a special case of Service that does not have An `ExternalName` Service is a special case of Service that does not have
selectors and uses DNS names instead. For more information, see the selectors and uses DNS names instead. For more information, see the
[ExternalName](#externalname) section later in this document. [ExternalName](#externalname) section.
### EndpointSlices ### EndpointSlices
@ -704,7 +709,7 @@ In a split-horizon DNS environment you would need two Services to be able to rou
and internal traffic to your endpoints. and internal traffic to your endpoints.
To set an internal load balancer, add one of the following annotations to your Service To set an internal load balancer, add one of the following annotations to your Service
depending on the cloud Service provider you're using. depending on the cloud service provider you're using:
{{< tabs name="service_tabs" >}} {{< tabs name="service_tabs" >}}
{{% tab name="Default" %}} {{% tab name="Default" %}}
@ -1151,9 +1156,9 @@ spec:
- name: http - name: http
protocol: TCP protocol: TCP
port: 80 port: 80
targetPort: 9376 targetPort: 49152
externalIPs: externalIPs:
- 80.11.12.10 - 198.51.100.32
``` ```
## Session stickiness ## Session stickiness
@ -1178,13 +1183,17 @@ mechanism Kubernetes provides to expose a Service with a virtual IP address.
## {{% heading "whatsnext" %}} ## {{% heading "whatsnext" %}}
Learn more about the following: Learn more about Services and how they fit into Kubernetes:
* Follow the [Connecting Applications with Services](/docs/tutorials/services/connect-applications-service/) tutorial * Follow the [Connecting Applications with Services](/docs/tutorials/services/connect-applications-service/) tutorial.
* [Ingress](/docs/concepts/services-networking/ingress/) exposes HTTP and HTTPS routes from outside the cluster to services within the cluster. * Read about [Ingress](/docs/concepts/services-networking/ingress/), which
* [EndpointSlices](/docs/concepts/services-networking/endpoint-slices/) exposes HTTP and HTTPS routes from outside the cluster to Services within
your cluster.
* Read about [Gateway](https://gateway-api.sigs.k8s.io/), an extension to
Kubernetes that provides more flexibility than Ingress.
For more context: For more context, read the following:
* [Virtual IPs and Service Proxies](/docs/reference/networking/virtual-ips/) * [Virtual IPs and Service Proxies](/docs/reference/networking/virtual-ips/)
* [API reference](/docs/reference/kubernetes-api/service-resources/service-v1/) for the Service API * [EndpointSlices](/docs/concepts/services-networking/endpoint-slices/)
* [API reference](/docs/reference/kubernetes-api/service-resources/endpoints-v1/) for the Endpoints API * [Service API reference](/docs/reference/kubernetes-api/service-resources/service-v1/)
* [API reference](/docs/reference/kubernetes-api/service-resources/endpoint-slice-v1/) for the EndpointSlice API * [EndpointSlice API reference](/docs/reference/kubernetes-api/service-resources/endpoint-slice-v1/)
* [Endpoint API reference (legacy)](/docs/reference/kubernetes-api/service-resources/endpoints-v1/)