Change:
<ins> --- title: Update API Objects in Place Using kubectl patch description: Use kubectl patch to update Kubernetes API objects in place. Do a strategic merge patch or a JSON merge patch. content_template: templates/task weight: 50 --- {{% capture overview %}} This task shows how to use `kubectl patch` to update an API object in place. The exercises in this task demonstrate a strategic merge patch and a JSON merge patch. {{% /capture %}} {{% capture prerequisites %}} {{< include "task-tutorial-prereqs.md" >}} {{< version-check >}} {{% /capture %}} {{% capture steps %}} ## Use a strategic merge patch to update a Deployment Here's the configuration file for a Deployment that has two replicas. Each replica is a Pod that has one container: {{< codenew file="application/deployment-patch.yaml" >}} Create the Deployment: ```shell kubectl apply -f https://k8s.io/examples/application/deployment-patch.yaml ``` View the Pods associated with your Deployment: ```shell kubectl get pods ``` The output shows that the Deployment has two Pods. The `1/1` indicates that each Pod has one container: ``` NAME                        READY     STATUS    RESTARTS   AGE patch-demo-28633765-670qr   1/1       Running   0          23s patch-demo-28633765-j5qs3   1/1       Running   0          23s ``` Make a note of the names of the running Pods. Later, you will see that these Pods get terminated and replaced by new ones. At this point, each Pod has one Container that runs the nginx image. Now suppose you want each Pod to have two containers: one that runs nginx and one that runs redis. Create a file named `patch-file.yaml` that has this content: ```yaml spec: template: spec: containers: - name: patch-demo-ctr-2 image: redis ``` Patch your Deployment: {{< tabs name="kubectl_patch_example" >}} {{{< tab name="Bash" codelang="bash" >}} kubectl patch deployment patch-demo --patch "$(cat patch-file.yaml)" {{< /tab >}} {{< tab name="PowerShell" codelang="posh" >}} kubectl patch deployment patch-demo --patch $(Get-Content patch-file.yaml -Raw) {{< /tab >}}} {{< /tabs >}} View the patched Deployment: ```shell kubectl get deployment patch-demo --output yaml ``` The output shows that the PodSpec in the Deployment has two Containers: ```shell containers: - image: redis imagePullPolicy: Always name: patch-demo-ctr-2 ... - image: nginx imagePullPolicy: Always name: patch-demo-ctr ... ``` View the Pods associated with your patched Deployment: ```shell kubectl get pods ``` The output shows that the running Pods have different names from the Pods that were running previously. The Deployment terminated the old Pods and created two new Pods that comply with the updated Deployment spec. The `2/2` indicates that each Pod has two Containers: ``` NAME                          READY     STATUS    RESTARTS   AGE patch-demo-1081991389-2wrn5   2/2       Running   0          1m patch-demo-1081991389-jmg7b   2/2       Running   0          1m ``` Take a closer look at one of the patch-demo Pods: ```shell kubectl get pod <your-pod-name> --output yaml ``` The output shows that the Pod has two Containers: one running nginx and one running redis: ``` containers: - image: redis ... - image: nginx ... ``` ### Notes on the strategic merge patch The patch you did in the preceding exercise is called a *strategic merge patch*. Notice that the patch did not replace the `containers` list. Instead it added a new Container to the list. In other words, the list in the patch was merged with the existing list. This is not always what happens when you use a strategic merge patch on a list. In some cases, the list is replaced, not merged. With a strategic merge patch, a list is either replaced or merged depending on its patch strategy. The patch strategy is specified by the value of the `patchStrategy` key in a field tag in the Kubernetes source code. For example, the `Containers` field of `PodSpec` struct has a `patchStrategy` of `merge`: ```go type PodSpec struct { ... Containers []Container `json:"containers" patchStrategy:"merge" patchMergeKey:"name" ...` ``` You can also see the patch strategy in the [OpenApi spec](https://raw.githubusercontent.com/kubernetes/kubernetes/master/api/openapi-spec/swagger.json): ```json "io.k8s.api.core.v1.PodSpec": { ... "containers": { "description": "List of containers belonging to the pod. ... }, "x-kubernetes-patch-merge-key": "name", "x-kubernetes-patch-strategy": "merge" }, ``` And you can see the patch strategy in the [Kubernetes API documentation](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#podspec-v1-core). Create a file named `patch-file-tolerations.yaml` that has this content: ```yaml spec: template: spec: tolerations: - effect: NoSchedule key: disktype value: ssd ``` Patch your Deployment: ```shell kubectl patch deployment patch-demo --patch "$(cat patch-file-tolerations.yaml)" ``` View the patched Deployment: ```shell kubectl get deployment patch-demo --output yaml ``` The output shows that the PodSpec in the Deployment has only one Toleration: ```shell tolerations: - effect: NoSchedule key: disktype value: ssd ``` Notice that the `tolerations` list in the PodSpec was replaced, not merged. This is because the Tolerations field of PodSpec does not have a `patchStrategy` key in its field tag. So the strategic merge patch uses the default patch strategy, which is `replace`. ```go type PodSpec struct { ... Tolerations []Toleration `json:"tolerations,omitempty" protobuf:"bytes,22,opt,name=tolerations"` ``` ## Use a JSON merge patch to update a Deployment A strategic merge patch is different from a [JSON merge patch](https://tools.ietf.org/html/rfc7386). With a JSON merge patch, if you want to update a list, you have to specify the entire new list. And the new list completely replaces the existing list. The `kubectl patch` command has a `type` parameter that you can set to one of these values: <table> <tr><th>Parameter value</th><th>Merge type</th></tr> <tr><td>json</td><td><a href="https://tools.ietf.org/html/rfc6902">JSON Patch, RFC 6902</a></td></tr> <tr><td>merge</td><td><a href="https://tools.ietf.org/html/rfc7386">JSON Merge Patch, RFC 7386</a></td></tr> <tr><td>strategic</td><td>Strategic merge patch</td></tr> </table> For a comparison of JSON patch and JSON merge patch, see [JSON Patch and JSON Merge Patch](http://erosb.github.io/post/json-patch-vs-merge-patch/). The default value for the `type` parameter is `strategic`. So in the preceding exercise, you did a strategic merge patch. Next, do a JSON merge patch on your same Deployment. Create a file named `patch-file-2.yaml` that has this content: ```yaml spec: template: spec: containers: - name: patch-demo-ctr-3 image: gcr.io/google-samples/node-hello:1.0 ``` In your patch command, set `type` to `merge`: ```shell kubectl patch deployment patch-demo --type merge --patch "$(cat patch-file-2.yaml)" ``` View the patched Deployment: ```shell kubectl get deployment patch-demo --output yaml ``` The `containers` list that you specified in the patch has only one Container. The output shows that your list of one Container replaced the existing `containers` list. ```shell spec: containers: - image: gcr.io/google-samples/node-hello:1.0 ... name: patch-demo-ctr-3 ``` List the running Pods: ```shell kubectl get pods ``` In the output, you can see that the existing Pods were terminated, and new Pods were created. The `1/1` indicates that each new Pod is running only one Container. ```shell NAME                          READY     STATUS    RESTARTS   AGE patch-demo-1307768864-69308   1/1       Running   0          1m patch-demo-1307768864-c86dc   1/1       Running   0          1m ``` ## Alternate forms of the kubectl patch command The `kubectl patch` command takes YAML or JSON. It can take the patch as a file or directly on the command line. Create a file named `patch-file.json` that has this content: ```json { "spec": { "template": { "spec": { "containers": [ { "name": "patch-demo-ctr-2", "image": "redis" } ] } } } } ``` The following commands are equivalent: ```shell kubectl patch deployment patch-demo --patch "$(cat patch-file.yaml)" kubectl patch deployment patch-demo --patch 'spec:n template:n  spec:n   containers:n   - name: patch-demo-ctr-2n     image: redis' kubectl patch deployment patch-demo --patch "$(cat patch-file.json)" kubectl patch deployment patch-demo --patch '{"spec": {"template": {"spec": {"containers": [{"name": "patch-demo-ctr-2","image": "redis"}]}}}}' ``` ## Summary In this exercise, you used `kubectl patch` to change the live configuration of a Deployment object. You did not change the configuration file that you originally used to create the Deployment object. Other commands for updating API objects include [kubectl annotate](/docs/reference/generated/kubectl/kubectl-commands/#annotate), [kubectl edit](/docs/reference/generated/kubectl/kubectl-commands/#edit), [kubectl replace](/docs/reference/generated/kubectl/kubectl-commands/#replace), [kubectl scale](/docs/reference/generated/kubectl/kubectl-commands/#scale), and [kubectl apply](/docs/reference/generated/kubectl/kubectl-commands/#apply). {{% /capture %}} {{% capture whatsnext %}} * [Kubernetes Object Management](/docs/concepts/overview/working-with-objects/object-management/) * [Managing Kubernetes Objects Using Imperative Commands](/docs/tasks/manage-kubernetes-objects/imperative-command/) * [Imperative Management of Kubernetes Objects Using Configuration Files](/docs/tasks/manage-kubernetes-objects/imperative-config/) * [Declarative Management of Kubernetes Objects Using Configuration Files](/docs/tasks/manage-kubernetes-objects/declarative-config/) {{% /capture %}} </ins>

Discussion:
This is a Feature Request We have a pretty good doc on various ways to patching an object: However, the current location of the content is wrong. It is not about an application. It is about more generic ways to change an API object. What would you like to be Revise and move the content to object management section so that readers would enjoy playing with the many ways of patching an object.
/assign
/kind cleanup /language en /priority backlog