Merge pull request #38562 from sftim/20221219_revise_service_concept_introduction

Revise introduction to Service page

Author: k8s-ci-robot

content/en/docs/concepts/services-networking/service.md

@@ -18,22 +18,23 @@ weight: 10
 
 {{< glossary_definition term_id="service" length="short" >}}
 
-With Kubernetes you don't need to modify your application to use an unfamiliar service discovery mechanism.
-Kubernetes gives Pods their own IP addresses and a single DNS name for a set of Pods,
-and can load-balance across them.
+A key aim of Services in Kubernetes is that you don't need to modify your existing
+application to use an unfamiliar service discovery mechanism.
+You can run code in Pods, whether this is a code designed for a cloud-native world, or
+an older app you've containerized. You use a Service to make that set of Pods available
+on the network so that clients can interact with it.
 
-<!-- body -->
-
-## Motivation
-
-Kubernetes {{< glossary_tooltip term_id="pod" text="Pods" >}} are created and destroyed
-to match the desired state of your cluster. Pods are nonpermanent resources.
 If you use a {{< glossary_tooltip term_id="deployment" >}} to run your app,
-it can create and destroy Pods dynamically.
+that Deployment can create and destroy Pods dynamically. From one moment to the next,
+you don't know how many of those Pods are working and healthy; you might not even know
+what those healthy Pods are named.
+Kubernetes {{< glossary_tooltip term_id="pod" text="Pods" >}} are created and destroyed
+to match the desired state of your cluster. Pods are emphemeral resources (you should not
+expect that an individual Pod is reliable and durable).
 
-Each Pod gets its own IP address, however in a Deployment, the set of Pods
-running in one moment in time could be different from
-the set of Pods running that application a moment later.
+Each Pod gets its own IP address (Kubernetes expects network plugins to ensure this).
+For a given Deployment in your cluster, the set of Pods running in one moment in
+time could be different from the set of Pods running that application a moment later.
 
 This leads to a problem: if some set of Pods (call them "backends") provides
 functionality to other Pods (call them "frontends") inside your cluster,
@@ -42,14 +43,13 @@ to, so that the frontend can use the backend part of the workload?
 
 Enter _Services_.
 
-## Service resources {#service-resource}
+<!-- body -->
 
-In Kubernetes, a Service is an abstraction which defines a logical set of Pods
-and a policy by which to access them (sometimes this pattern is called
-a micro-service). The set of Pods targeted by a Service is usually determined
-by a {{< glossary_tooltip text="selector" term_id="selector" >}}.
-To learn about other ways to define Service endpoints,
-see [Services _without_ selectors](#services-without-selectors).
+## Services in Kubernetes
+
+The Service API, part of Kubernetes, is an abstraction to help you expose groups of
+Pods over a network. Each Service object defines a logical set of endpoints (usually
+these endpoints are Pods) along with a policy about how to make those pods accessible.
 
 For example, consider a stateless image-processing backend which is running with
 3 replicas.  Those replicas are fungible&mdash;frontends do not care which backend
@@ -59,6 +59,26 @@ track of the set of backends themselves.
 
 The Service abstraction enables this decoupling.
 
+The set of Pods targeted by a Service is usually determined
+by a {{< glossary_tooltip text="selector" term_id="selector" >}} that you
+define.
+To learn about other ways to define Service endpoints,
+see [Services _without_ selectors](#services-without-selectors).
+
+If your workload speaks HTTP, you might choose to use an
+[Ingress](/docs/concepts/services-networking/ingress/) to control how web traffic
+reaches that workload.
+Ingress is not a Service type, but it acts as the entry point for your
+cluster. An Ingress lets you consolidate your routing rules into a single resource, so
+that you can expose multiple components of your workload, running separately in your
+cluster, behind a single listener.
+
+The [Gateway](https://gateway-api.sigs.k8s.io/#what-is-the-gateway-api) API for Kubernetes
+provides extra capabilities beyond Ingress and Service. You can add Gateway to your cluster -
+it is a family of extension APIs, implemented using
+{{< glossary_tooltip term_id="CustomResourceDefinition" text="CustomResourceDefinitions" >}} -
+and then use these to configure access to network services that are running in your cluster.
+
 ### Cloud-native service discovery
 
 If you're able to use Kubernetes APIs for service discovery in your application,
@@ -69,6 +89,9 @@ whenever the set of Pods in a Service changes.
 For non-native applications, Kubernetes offers ways to place a network port or load
 balancer in between your application and the backend Pods.
 
+Either way, your workload can use these [service discovery](#discovering-services)
+mechanisms to find the target it wants to connect to.
+
 ## Defining a Service
 
 A Service in Kubernetes is an