433 lines
19 KiB
Markdown
433 lines
19 KiB
Markdown
---
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---
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You've deployed your application and exposed it via a service. Now what? Kubernetes provides a number of tools to help you manage your application deployment, including scaling and updating. Among the features we'll discuss in more depth are [configuration files](/docs/user-guide/configuring-containers/#configuration-in-kubernetes) and [labels](/docs/user-guide/deploying-applications/#labels).
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You can find all the files for this example [in our docs
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repo here](https://github.com/kubernetes/kubernetes.github.io/tree/{{page.docsbranch}}/docs/user-guide/).
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* TOC
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{:toc}
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## Organizing resource configurations
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Many applications require multiple resources to be created, such as a Deployment and a Service. Management of multiple resources can be simplified by grouping them together in the same file (separated by `---` in YAML). For example:
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{% include code.html language="yaml" file="nginx-app.yaml" ghlink="/docs/user-guide/nginx-app.yaml" %}
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Multiple resources can be created the same way as a single resource:
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```shell
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$ kubectl create -f docs/user-guide/nginx-app.yaml
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service "my-nginx-svc" created
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deployment "my-nginx" created
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```
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The resources will be created in the order they appear in the file. Therefore, it's best to specify the service first, since that will ensure the scheduler can spread the pods associated with the service as they are created by the controller(s), such as Deployment.
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`kubectl create` also accepts multiple `-f` arguments:
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```shell
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$ kubectl create -f docs/user-guide/nginx/nginx-svc.yaml -f docs/user-guide/nginx/nginx-deployment.yaml
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```
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And a directory can be specified rather than or in addition to individual files:
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```shell
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$ kubectl create -f docs/user-guide/nginx/
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```
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`kubectl` will read any files with suffixes `.yaml`, `.yml`, or `.json`.
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It is a recommended practice to put resources related to the same microservice or application tier into the same file, and to group all of the files associated with your application in the same directory. If the tiers of your application bind to each other using DNS, then you can then simply deploy all of the components of your stack en masse.
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A URL can also be specified as a configuration source, which is handy for deploying directly from configuration files checked into github:
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```shell
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$ kubectl create -f https://raw.githubusercontent.com/kubernetes/kubernetes/master/docs/user-guide/nginx-deployment.yaml
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deployment "nginx-deployment" created
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```
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## Bulk operations in kubectl
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Resource creation isn't the only operation that `kubectl` can perform in bulk. It can also extract resource names from configuration files in order to perform other operations, in particular to delete the same resources you created:
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```shell
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$ kubectl delete -f docs/user-guide/nginx/
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deployment "my-nginx" deleted
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service "my-nginx-svc" deleted
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```
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In the case of just two resources, it's also easy to specify both on the command line using the resource/name syntax:
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```shell
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$ kubectl delete deployments/my-nginx services/my-nginx-svc
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```
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For larger numbers of resources, you'll find it easier to specify the selector (label query) specified using `-l` or `--selector`, to filter resources by their labels:
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```shell
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$ kubectl delete deployment,services -l app=nginx
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deployment "my-nginx" deleted
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service "my-nginx-svc" deleted
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```
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Because `kubectl` outputs resource names in the same syntax it accepts, it's easy to chain operations using `$()` or `xargs`:
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```shell
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$ kubectl get $(k create -f docs/user-guide/nginx/ -o name | grep service)
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NAME CLUSTER-IP EXTERNAL-IP PORT(S) AGE
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my-nginx-svc 10.0.0.208 80/TCP 0s
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```
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With the above commands, we first create resources under docs/user-guide/nginx/ and print the resources created with `-o name` output format
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(print each resource as resource/name). Then we `grep` only the "service", and then print it with `kubectl get`.
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If you happen to organize your resources across several subdirectories within a particular directory, you can recursively perform the operations on the subdirectories also, by specifying `--recursive` or `-R` alongside the `--filename,-f` flag.
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For instance, assume there is a directory `project/k8s/development` that holds all of the manifests needed for the development environment, organized by resource type:
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```
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project/k8s/development
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├── configmap
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│ └── my-configmap.yaml
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├── deployment
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│ └── my-deployment.yaml
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└── pvc
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└── my-pvc.yaml
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```
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By default, performing a bulk operation on `project/k8s/development` will stop at the first level of the directory, not processing any subdirectories. If we tried to create the resources in this directory using the following command, we'd encounter an error:
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```shell
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$ kubectl create -f project/k8s/development
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error: you must provide one or more resources by argument or filename (.json|.yaml|.yml|stdin)
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```
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Instead, specify the `--recursive` or `-R` flag with the `--filename,-f` flag as such:
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```shell
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$ kubectl create -f project/k8s/development --recursive
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configmap "my-config" created
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deployment "my-deployment" created
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persistentvolumeclaim "my-pvc" created
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```
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The `--recursive` flag works with any operation that accepts the `--filename,-f` flag such as: `kubectl {create,get,delete,describe,rollout} etc.`
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The `--recursive` flag also works when multiple `-f` arguments are provided:
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```shell
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$ kubectl create -f project/k8s/namespaces -f project/k8s/development --recursive
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namespace "development" created
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namespace "staging" created
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configmap "my-config" created
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deployment "my-deployment" created
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persistentvolumeclaim "my-pvc" created
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```
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If you're interested in learning more about `kubectl`, go ahead and read [kubectl Overview](/docs/user-guide/kubectl-overview).
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## Using labels effectively
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The examples we've used so far apply at most a single label to any resource. There are many scenarios where multiple labels should be used to distinguish sets from one another.
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For instance, different applications would use different values for the `app` label, but a multi-tier application, such as the [guestbook example](https://github.com/kubernetes/kubernetes/tree/{{page.githubbranch}}/examples/guestbook/), would additionally need to distinguish each tier. The frontend could carry the following labels:
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```yaml
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labels:
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app: guestbook
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tier: frontend
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```
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while the Redis master and slave would have different `tier` labels, and perhaps even an additional `role` label:
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```yaml
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labels:
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app: guestbook
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tier: backend
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role: master
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```
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and
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```yaml
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labels:
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app: guestbook
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tier: backend
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role: slave
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```
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The labels allow us to slice and dice our resources along any dimension specified by a label:
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```shell
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$ kubectl create -f examples/guestbook/all-in-one/guestbook-all-in-one.yaml
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$ kubectl get pods -Lapp -Ltier -Lrole
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NAME READY STATUS RESTARTS AGE APP TIER ROLE
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guestbook-fe-4nlpb 1/1 Running 0 1m guestbook frontend <none>
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guestbook-fe-ght6d 1/1 Running 0 1m guestbook frontend <none>
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guestbook-fe-jpy62 1/1 Running 0 1m guestbook frontend <none>
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guestbook-redis-master-5pg3b 1/1 Running 0 1m guestbook backend master
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guestbook-redis-slave-2q2yf 1/1 Running 0 1m guestbook backend slave
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guestbook-redis-slave-qgazl 1/1 Running 0 1m guestbook backend slave
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my-nginx-divi2 1/1 Running 0 29m nginx <none> <none>
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my-nginx-o0ef1 1/1 Running 0 29m nginx <none> <none>
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$ kubectl get pods -lapp=guestbook,role=slave
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NAME READY STATUS RESTARTS AGE
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guestbook-redis-slave-2q2yf 1/1 Running 0 3m
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guestbook-redis-slave-qgazl 1/1 Running 0 3m
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```
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## Canary deployments
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Another scenario where multiple labels are needed is to distinguish deployments of different releases or configurations of the same component. It is common practice to deploy a *canary* of a new application release (specified via image tag in the pod template) side by side with the previous release so that the new release can receive live production traffic before fully rolling it out.
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For instance, you can use a `track` label to differentiate different releases.
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The primary, stable release would have a `track` label with value as `stable`:
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```yaml
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name: frontend
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replicas: 3
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...
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labels:
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app: guestbook
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tier: frontend
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track: stable
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...
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image: gb-frontend:v3
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```
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and then you can create a new release of the guestbook frontend that carries the `track` label with different value (i.e. `canary`), so that two sets of pods would not overlap:
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```yaml
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name: frontend-canary
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replicas: 1
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...
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labels:
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app: guestbook
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tier: frontend
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track: canary
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...
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image: gb-frontend:v4
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```
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The frontend service would span both sets of replicas by selecting the common subset of their labels (i.e. omitting the `track` label), so that the traffic will be redirected to both applications:
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```yaml
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selector:
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app: guestbook
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tier: frontend
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```
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You can tweak the number of replicas of the stable and canary releases to determine the ratio of each release that will receive live production traffic (in this case, 3:1).
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Once you're confident, you can update the stable track to the new application release and remove the canary one.
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For a more concrete example, check the [tutorial of deploying Ghost](https://github.com/kelseyhightower/talks/tree/master/kubecon-eu-2016/demo#deploy-a-canary).
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## Updating labels
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Sometimes existing pods and other resources need to be relabeled before creating new resources. This can be done with `kubectl label`.
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For example, if you want to label all your nginx pods as frontend tier, simply run:
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```shell
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$ kubectl label pods -l app=nginx tier=fe
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pod "my-nginx-2035384211-j5fhi" labeled
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pod "my-nginx-2035384211-u2c7e" labeled
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pod "my-nginx-2035384211-u3t6x" labeled
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```
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This first filters all pods with the label "app=nginx", and then labels them with the "tier=fe".
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To see the pods you just labeled, run:
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```shell
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$ kubectl get pods -l app=nginx -L tier
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NAME READY STATUS RESTARTS AGE TIER
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my-nginx-2035384211-j5fhi 1/1 Running 0 23m fe
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my-nginx-2035384211-u2c7e 1/1 Running 0 23m fe
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my-nginx-2035384211-u3t6x 1/1 Running 0 23m fe
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```
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This outputs all "app=nginx" pods, with an additional label column of pods' tier (specified with `-L` or `--label-columns`).
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For more information, please see [labels](/docs/user-guide/labels/) and [kubectl label](/docs/user-guide/kubectl/kubectl_label/) document.
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## Updating annotations
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Sometimes you would want to attach annotations to resources. Annotations are arbitrary non-identifying metadata for retrieval by API clients such as tools, libraries, etc. This can be done with `kubectl annotate`. For example:
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```shell
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$ kubectl annotate pods my-nginx-v4-9gw19 description='my frontend running nginx'
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$ kubectl get pods my-nginx-v4-9gw19 -o yaml
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apiversion: v1
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kind: pod
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metadata:
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annotations:
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description: my frontend running nginx
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...
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```
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For more information, please see [annotations](/docs/user-guide/annotations/) and [kubectl annotate](/docs/user-guide/kubectl/kubectl_annotate/) document.
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## Scaling your application
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When load on your application grows or shrinks, it's easy to scale with `kubectl`. For instance, to decrease the number of nginx replicas from 3 to 1, do:
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```shell
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$ kubectl scale deployment/my-nginx --replicas=1
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deployment "my-nginx" scaled
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```
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Now you only have one pod managed by the deployment.
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```shell
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$ kubectl get pods -l app=nginx
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NAME READY STATUS RESTARTS AGE
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my-nginx-2035384211-j5fhi 1/1 Running 0 30m
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```
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To have the system automatically choose the number of nginx replicas as needed, ranging from 1 to 3, do:
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```shell
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$ kubectl autoscale deployment/my-nginx --min=1 --max=3
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deployment "my-nginx" autoscaled
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```
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Now your nginx replicas will be scaled up and down as needed, automatically.
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For more information, please see [kubectl scale](/docs/user-guide/kubectl/kubectl_scale/), [kubectl autoscale](/docs/user-guide/kubectl/kubectl_autoscale/) and [horizontal pod autoscaler](/docs/user-guide/horizontal-pod-autoscaler/) document.
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## In-place updates of resources
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Sometimes it's necessary to make narrow, non-disruptive updates to resources you've created.
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### kubectl apply
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It is suggested to maintain a set of configuration files in source control (see [configuration as code](http://martinfowler.com/bliki/InfrastructureAsCode.html)),
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so that they can be maintained and versioned along with the code for the resources they configure.
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Then, you can use [`kubectl apply`](/docs/user-guide/kubectl/kubectl_apply/) to push your configuration changes to the cluster.
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This command will compare the version of the configuration that you're pushing with the previous version and apply the changes you've made, without overwriting any automated changes to properties you haven't specified.
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```shell
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$ kubectl apply -f docs/user-guide/nginx/nginx-deployment.yaml
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deployment "my-nginx" configured
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```
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Note that `kubectl apply` attaches an annotation to the resource in order to determine the changes to the configuration since the previous invocation. When it's invoked, `kubectl apply` does a three-way diff between the previous configuration, the provided input and the current configuration of the resource, in order to determine how to modify the resource.
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Currently, resources are created without this annotation, so the first invocation of `kubectl apply` will fall back to a two-way diff between the provided input and the current configuration of the resource. During this first invocation, it cannot detect the deletion of properties set when the resource was created. For this reason, it will not remove them.
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All subsequent calls to `kubectl apply`, and other commands that modify the configuration, such as `kubectl replace` and `kubectl edit`, will update the annotation, allowing subsequent calls to `kubectl apply` to detect and perform deletions using a three-way diff.
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**Note:** To use apply, always create resource initially with either `kubectl apply` or `kubectl create --save-config`.
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### kubectl edit
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Alternatively, you may also update resources with `kubectl edit`:
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```shell
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$ kubectl edit deployment/my-nginx
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```
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This is equivalent to first `get` the resource, edit it in text editor, and then `apply` the resource with the updated version:
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```shell
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$ kubectl get deployment my-nginx -o yaml > /tmp/nginx.yaml
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$ vi /tmp/nginx.yaml
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# do some edit, and then save the file
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$ kubectl apply -f /tmp/nginx.yaml
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deployment "my-nginx" configured
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$ rm /tmp/nginx.yaml
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```
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This allows you to do more significant changes more easily. Note that you can specify the editor with your `EDITOR` or `KUBE_EDITOR` environment variables.
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For more information, please see [kubectl edit](/docs/user-guide/kubectl/kubectl_edit/) document.
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### kubectl patch
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Suppose you want to fix a typo of the container's image of a Deployment. One way to do that is with `kubectl patch`:
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```shell
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# Suppose you have a Deployment with a container named "nginx" and its image "nignx" (typo),
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# use container name "nginx" as a key to update the image from "nignx" (typo) to "nginx"
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$ kubectl get deployment my-nginx -o yaml
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```
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```yaml
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apiVersion: extensions/v1beta1
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kind: Deployment
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...
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spec:
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template:
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spec:
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containers:
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- image: nignx
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name: nginx
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...
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```
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```shell
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$ kubectl patch deployment my-nginx -p'{"spec":{"template":{"spec":{"containers":[{"name":"nginx","image":"nginx"}]}}}}'
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"my-nginx" patched
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$ kubectl get pod my-nginx-1jgkf -o yaml
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```
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```yaml
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apiVersion: extensions/v1beta1
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kind: Deployment
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...
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spec:
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template:
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spec:
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containers:
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- image: nginx
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name: nginx
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...
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```
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The patch is specified using json.
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The system ensures that you don’t clobber changes made by other users or components by confirming that the `resourceVersion` doesn’t differ from the version you edited. If you want to update regardless of other changes, remove the `resourceVersion` field when you edit the resource. However, if you do this, don’t use your original configuration file as the source since additional fields most likely were set in the live state.
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For more information, please see [kubectl patch](/docs/user-guide/kubectl/kubectl_patch/) document.
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## Disruptive updates
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In some cases, you may need to update resource fields that cannot be updated once initialized, or you may just want to make a recursive change immediately, such as to fix broken pods created by a Deployment. To change such fields, use `replace --force`, which deletes and re-creates the resource. In this case, you can simply modify your original configuration file:
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```shell
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$ kubectl replace -f docs/user-guide/nginx/nginx-deployment.yaml --force
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deployment "my-nginx" deleted
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deployment "my-nginx" replaced
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```
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## Updating your application without a service outage
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At some point, you'll eventually need to update your deployed application, typically by specifying a new image or image tag, as in the canary deployment scenario above. `kubectl` supports several update operations, each of which is applicable to different scenarios.
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We'll guide you through how to create and update applications with Deployments. If your deployed application is managed by Replication Controllers,
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you should read [how to use `kubectl rolling-update`](/docs/user-guide/rolling-updates/) instead.
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Let's say you were running version 1.7.9 of nginx:
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```shell
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$ kubectl run my-nginx --image=nginx:1.7.9 --replicas=3
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deployment "my-nginx" created
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```
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To update to version 1.9.1, simply change `.spec.template.spec.containers[0].image` from `nginx:1.7.9` to `nginx:1.9.1`, with the kubectl commands we learned above.
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```shell
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$ kubectl edit deployment/my-nginx
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```
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That's it! The Deployment will declaratively update the deployed nginx application progressively behind the scene. It ensures that only a certain number of old replicas may be down while they are being updated, and only a certain number of new replicas may be created above the desired number of pods. To learn more details about it, visit [Deployment page](/docs/user-guide/deployments/).
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## What's next?
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- [Learn about how to use `kubectl` for application introspection and debugging.](/docs/user-guide/introspection-and-debugging/)
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- [Configuration Best Practices and Tips](/docs/user-guide/config-best-practices/)
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