add federation job doc (#5485)

* add federation job doc

* Update job.md

Edits for clarity and consistency

* Update job.md

Fixed a typo

docs/tasks/administer-federation/job.md

@@ -0,0 +1,102 @@
+---
+title: Federated Jobs
+---
+
+{% capture overview %}
+This guide explains how to use jobs in the federation control plane.
+
+Jobs in the federation control plane (referred to as "federated jobs" in
+this guide) are similar to the traditional [Kubernetes
+jobs](/docs/concepts/workloads/controllers/job/), and provide the same functionality.
+Creating jobs in the federation control plane ensures that the desired number of
+parallelism and completions exist across the registered clusters.
+{% endcapture %}
+
+{% capture prerequisites %}
+
+* {% include federated-task-tutorial-prereqs.md %}
+* You are also expected to have a basic
+[working knowledge of Kubernetes](/docs/getting-started-guides/) in
+general and [jobs](/docs/concepts/workloads/controllers/jobs-run-to-completion/) in particular.
+{% endcapture %}
+
+{% capture steps %}
+
+## Creating a federated job
+
+The API for federated jobs is fully compatible with the
+API for traditional Kubernetes jobs. You can create a job by sending
+a request to the federation apiserver.
+
+You can do that using [kubectl](/docs/user-guide/kubectl/) by running:
+
+``` shell
+kubectl --context=federation-cluster create -f myjob.yaml
+```
+
+The '--context=federation-cluster' flag tells kubectl to submit the
+request to the federation API server instead of sending it to a Kubernetes
+cluster.
+
+Once a federated job is created, the federation control plane creates
+a job in all underlying Kubernetes clusters.
+You can verify this by checking each of the underlying clusters, for example:
+
+``` shell
+kubectl --context=gce-asia-east1a get job myjob
+```
+
+The previous example assumes that you have a context named `gce-asia-east1a`
+configured in your client for your cluster in that zone.
+
+The jobs in the underlying clusters match the federated job
+except in the number of parallelism and completions. The federation control plane ensures that the
+sum of the parallelism and completions in each cluster matches the desired number of parallelism and completions in the
+federated job.
+
+### Spreading job tasks in underlying clusters
+
+By default, parallelism and completions are spread equally in all underlying clusters. For example:
+if you have 3 registered clusters and you create a federated job with
+`spec.parallelism = 9` and `spec.completions = 18`, then each job in the 3 clusters has
+`spec.parallelism = 3` and `spec.completions = 6`.
+To modify the number of parallelism and completions in each cluster, you can specify
+[ReplicaAllocationPreferences](https://github.com/kubernetes/kubernetes/blob/{{page.githubbranch}}/federation/apis/federation/types.go)
+as an annotation with key `federation.kubernetes.io/job-preferences`
+on the federated job.
+
+
+## Updating a federated job
+
+You can update a federated job as you would update a Kubernetes
+job; however, for a federated job, you must send the request to
+the federation API server instead of sending it to a specific Kubernetes cluster.
+The federation control plane ensures that whenever the federated job is
+updated, it updates the corresponding job in all underlying clusters to
+match it.
+
+If your update includes a change in number of parallelism and completions, the federation
+control plane changes the number of parallelism and completions in underlying clusters to
+ensure that their sum remains equal to the number of desired parallelism and completions in
+federated job.
+
+## Deleting a federated job
+
+You can delete a federated job as you would delete a Kubernetes
+job; however, for a federated job, you must send the request to
+the federation API server instead of sending it to a specific Kubernetes cluster.
+
+For example, with kubectl:
+
+```shell
+kubectl --context=federation-cluster delete job myjob
+```
+
+**Note:** Deleting a federated job will not delete the
+corresponding jobs from underlying clusters.
+You must delete the underlying jobs manually.
+{: .note}
+
+{% endcapture %}
+
+{% include templates/task.md %}