add Usage example for Demo

README.md

@@ -17,7 +17,7 @@ Take a look at the [concepts](https://jobset.sigs.k8s.io/docs/concepts/) page fo
 
 - **Support for multi-template jobs**: JobSet models a distributed training workload as a group of K8s Jobs. This allows a user to easily specify different pod templates for different distinct groups of pods (e.g. a leader, workers, parameter servers, etc.), something which cannot be done by a single Job.
 
-  - **Automatic headless service configuration and lifecycle management**: ML and HPC frameworks require a stable network endpoint for each worker in the distributed workload, and since pod IPs are dynamically assigned and can change between restarts, stable pod hostnames are required for distributed training on k8s, By default, JobSet uses [IndexedJobs](https://kubernetes.io/blog/2021/04/19/introducing-indexed-jobs/) to establish stable pod hostnames, and does automatic configuration and lifecycle management of the headless service to trigger DNS record creations and establish network connectivity via pod hostnames.You can run this [example](./examples/simple/jobset-with-network.yaml) yourself to see how exclusive placement works.
+- **Automatic headless service configuration and lifecycle management**: ML and HPC frameworks require a stable network endpoint for each worker in the distributed workload, and since pod IPs are dynamically assigned and can change between restarts, stable pod hostnames are required for distributed training on k8s, By default, JobSet uses [IndexedJobs](https://kubernetes.io/blog/2021/04/19/introducing-indexed-jobs/) to establish stable pod hostnames, and does automatic configuration and lifecycle management of the headless service to trigger DNS record creations and establish network connectivity via pod hostnames.You can run this [example](examples/network-policy/jobset-with-network.yaml) yourself to see how exclusive placement works.
 
 - **Configurable success policies**: JobSet has [configurable success policies](https://github.com/kubernetes-sigs/jobset/blob/v0.5.0/examples/simple/success-policy.yaml) which target specific ReplicatedJobs, with operators to target `Any` or `All` of their child jobs. For example, you can configure the JobSet to be marked complete if and only if all pods that are part of the “worker” ReplicatedJob are completed. This enables users to use their compute resources more efficiently, allowing a workload to be declared successful and release the resources for the next workload more quickly.
 

examples/network-policy/README.md

@@ -0,0 +1,48 @@
+## Usage example
+### Purpose
+This document provides an example of achieving communication between different pods using a headless service with JobSet.
+
+- apply and check whether the jobset's pod and svc start normally
+```bash
+root@VM-0-4-ubuntu:/home/ubuntu# vi jobset-network.yaml
+root@VM-0-4-ubuntu:/home/ubuntu# kubectl apply -f jobset-network.yaml
+jobset.jobset.x-k8s.io/network-jobset created
+root@VM-0-4-ubuntu:/home/ubuntu# kubectl get pods
+NAME                               READY   STATUS    RESTARTS   AGE   IP          NODE               NOMINATED NODE   READINESS GATES
+network-jobset-leader-0-0-5xnzz    1/1     Running   0          17m   10.6.2.27   cluster1-worker    <none>           <none>
+network-jobset-workers-0-0-78k9j   1/1     Running   0          17m   10.6.1.16   cluster1-worker2   <none>           <none>
+network-jobset-workers-0-1-rmw42   1/1     Running   0          17m   10.6.2.28   cluster1-worker    <none>           <none>
+root@VM-0-4-ubuntu:/home/ubuntu# kubectl get svc
+NAME         TYPE        CLUSTER-IP   EXTERNAL-IP   PORT(S)   AGE
+example      ClusterIP   None         <none>        <none>    19s
+kubernetes   ClusterIP   10.96.0.1    <none>        443/TCP   2d1h
+```
+- Use the exec command to enter the container
+- We can first check the /etc/hosts file in the container. We can see that there is a domain name, such as: network-jobset-leader-0-0.example.default.svc.cluster.local
+- Other containers can access the current pod through this domain name. In the same way, we can also access the domain names of other pods for network communication.
+- For example: we can access the pods of network-jobset-workers-0-0-78k9j and network-jobset-workers-0-1-rmw42 respectively
+```bash
+root@VM-0-4-ubuntu:/home/ubuntu# kubectl exec -it network-jobset-leader-0-0-5xnzz -- sh
+/ # cat /etc/hosts
+# Kubernetes-managed hosts file.
+127.0.0.1	localhost
+...
+10.6.2.27	network-jobset-leader-0-0.example.default.svc.cluster.local	network-jobset-leader-0-0
+/ # ping network-jobset-workers-0-.example.default.svc.cluster.local
+ping: bad address 'network-jobset-workers-0-.example.default.svc.cluster.local'
+/ # ping network-jobset-workers-0-0.example.default.svc.cluster.local
+PING network-jobset-workers-0-0.example.default.svc.cluster.local (10.6.1.16): 56 data bytes
+64 bytes from 10.6.1.16: seq=0 ttl=62 time=0.121 ms
+64 bytes from 10.6.1.16: seq=1 ttl=62 time=0.093 ms
+64 bytes from 10.6.1.16: seq=2 ttl=62 time=0.094 ms
+64 bytes from 10.6.1.16: seq=3 ttl=62 time=0.103 ms
+--- network-jobset-workers-0-0.example.default.svc.cluster.local ping statistics ---
+4 packets transmitted, 4 packets received, 0% packet loss
+round-trip min/avg/max = 0.093/0.102/0.121 ms
+/ # ping network-jobset-workers-0-1.example.default.svc.cluster.local
+PING network-jobset-workers-0-1.example.default.svc.cluster.local (10.6.2.28): 56 data bytes
+64 bytes from 10.6.2.28: seq=0 ttl=63 time=0.068 ms
+64 bytes from 10.6.2.28: seq=1 ttl=63 time=0.072 ms
+64 bytes from 10.6.2.28: seq=2 ttl=63 time=0.079 ms
+--- network-jobset-workers-0-1.example.default.svc.cluster.local ping statistics ---
+```