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title: Melhores Práticas de Configuração
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content_type: concept
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weight: 10
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---
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<!-- overview -->
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Esse documento destaca e consolida as melhores práticas de configuração apresentadas em todo o guia de usuário,
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na documentação de introdução e nos exemplos.
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Este é um documento vivo. Se você pensar em algo que não está nesta lista, mas pode ser útil para outras pessoas,
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não hesite em criar uma *issue* ou submeter um PR.
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<!-- body -->
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## Dicas Gerais de Configuração
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- Ao definir configurações, especifique a versão mais recente estável da API.
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- Os arquivos de configuração devem ser armazenados em um sistema de controle antes de serem enviados ao cluster.
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Isso permite que você reverta rapidamente uma alteração de configuração, caso necessário. Isso também auxilia na recriação e restauração do cluster.
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- Escreva seus arquivos de configuração usando YAML ao invés de JSON. Embora esses formatos possam ser usados alternadamente em quase todos os cenários, YAML tende a ser mais amigável.
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- Agrupe objetos relacionados em um único arquivo sempre que fizer sentido. Geralmente, um arquivo é mais fácil de
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gerenciar do que vários. Veja o [guestbook-all-in-one.yaml](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/guestbook/all-in-one/guestbook-all-in-one.yaml) como exemplo dessa sintaxe.
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- Observe também que vários comandos `kubectl` podem ser chamados em um diretório. Por exemplo, você pode chamar
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`kubectl apply` em um diretório de arquivos de configuração.
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- Não especifique valores padrões desnecessariamente: configurações simples e mínimas diminuem a possibilidade de erros.
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- Coloque descrições de objetos nas anotações para permitir uma melhor análise.
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## "Naked" Pods versus ReplicaSets, Deployments, and Jobs {#naked-pods-vs-replicasets-deployments-and-jobs}
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- Don't use naked Pods (that is, Pods not bound to a [ReplicaSet](/docs/concepts/workloads/controllers/replicaset/) or [Deployment](/docs/concepts/workloads/controllers/deployment/)) if you can avoid it. Naked Pods will not be rescheduled in the event of a node failure.
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A Deployment, which both creates a ReplicaSet to ensure that the desired number of Pods is always available, and specifies a strategy to replace Pods (such as [RollingUpdate](/docs/concepts/workloads/controllers/deployment/#rolling-update-deployment)), is almost always preferable to creating Pods directly, except for some explicit [`restartPolicy: Never`](/docs/concepts/workloads/pods/pod-lifecycle/#restart-policy) scenarios. A [Job](/docs/concepts/workloads/controllers/job/) may also be appropriate.
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## Services
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- Create a [Service](/docs/concepts/services-networking/service/) before its corresponding backend workloads (Deployments or ReplicaSets), and before any workloads that need to access it. When Kubernetes starts a container, it provides environment variables pointing to all the Services which were running when the container was started. For example, if a Service named `foo` exists, all containers will get the following variables in their initial environment:
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```shell
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FOO_SERVICE_HOST=<the host the Service is running on>
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FOO_SERVICE_PORT=<the port the Service is running on>
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```
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*This does imply an ordering requirement* - any `Service` that a `Pod` wants to access must be created before the `Pod` itself, or else the environment variables will not be populated. DNS does not have this restriction.
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- An optional (though strongly recommended) [cluster add-on](/docs/concepts/cluster-administration/addons/) is a DNS server. The
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DNS server watches the Kubernetes API for new `Services` and creates a set of DNS records for each. If DNS has been enabled throughout the cluster then all `Pods` should be able to do name resolution of `Services` automatically.
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- Don't specify a `hostPort` for a Pod unless it is absolutely necessary. When you bind a Pod to a `hostPort`, it limits the number of places the Pod can be scheduled, because each <`hostIP`, `hostPort`, `protocol`> combination must be unique. If you don't specify the `hostIP` and `protocol` explicitly, Kubernetes will use `0.0.0.0` as the default `hostIP` and `TCP` as the default `protocol`.
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If you only need access to the port for debugging purposes, you can use the [apiserver proxy](/docs/tasks/access-application-cluster/access-cluster/#manually-constructing-apiserver-proxy-urls) or [`kubectl port-forward`](/docs/tasks/access-application-cluster/port-forward-access-application-cluster/).
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If you explicitly need to expose a Pod's port on the node, consider using a [NodePort](/docs/concepts/services-networking/service/#nodeport) Service before resorting to `hostPort`.
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- Avoid using `hostNetwork`, for the same reasons as `hostPort`.
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- Use [headless Services](/docs/concepts/services-networking/service/#headless-services) (which have a `ClusterIP` of `None`) for service discovery when you don't need `kube-proxy` load balancing.
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## Using Labels
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- Define and use [labels](/docs/concepts/overview/working-with-objects/labels/) that identify __semantic attributes__ of your application or Deployment, such as `{ app: myapp, tier: frontend, phase: test, deployment: v3 }`. You can use these labels to select the appropriate Pods for other resources; for example, a Service that selects all `tier: frontend` Pods, or all `phase: test` components of `app: myapp`. See the [guestbook](https://github.com/kubernetes/examples/tree/{{< param "githubbranch" >}}/guestbook/) app for examples of this approach.
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A Service can be made to span multiple Deployments by omitting release-specific labels from its selector. When you need to update a running service without downtime, use a [Deployment](/docs/concepts/workloads/controllers/deployment/).
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A desired state of an object is described by a Deployment, and if changes to that spec are _applied_, the deployment controller changes the actual state to the desired state at a controlled rate.
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- Use the [Kubernetes common labels](/docs/concepts/overview/working-with-objects/common-labels/) for common use cases. These standardized labels enrich the metadata in a way that allows tools, including `kubectl` and [dashboard](/docs/tasks/access-application-cluster/web-ui-dashboard), to work in an interoperable way.
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- You can manipulate labels for debugging. Because Kubernetes controllers (such as ReplicaSet) and Services match to Pods using selector labels, removing the relevant labels from a Pod will stop it from being considered by a controller or from being served traffic by a Service. If you remove the labels of an existing Pod, its controller will create a new Pod to take its place. This is a useful way to debug a previously "live" Pod in a "quarantine" environment. To interactively remove or add labels, use [`kubectl label`](/docs/reference/generated/kubectl/kubectl-commands#label).
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## Container Images
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The [imagePullPolicy](/docs/concepts/containers/images/#updating-images) and the tag of the image affect when the [kubelet](/docs/reference/command-line-tools-reference/kubelet/) attempts to pull the specified image.
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- `imagePullPolicy: IfNotPresent`: the image is pulled only if it is not already present locally.
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- `imagePullPolicy: Always`: every time the kubelet launches a container, the kubelet queries the container image registry to resolve the name to an image digest. If the kubelet has a container image with that exact digest cached locally, the kubelet uses its cached image; otherwise, the kubelet downloads (pulls) the image with the resolved digest, and uses that image to launch the container.
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- `imagePullPolicy` is omitted and either the image tag is `:latest` or it is omitted: `imagePullPolicy` is automatically set to `Always`. Note that this will _not_ be updated to `IfNotPresent` if the tag changes value.
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- `imagePullPolicy` is omitted and the image tag is present but not `:latest`: `imagePullPolicy` is automatically set to `IfNotPresent`. Note that this will _not_ be updated to `Always` if the tag is later removed or changed to `:latest`.
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- `imagePullPolicy: Never`: the image is assumed to exist locally. No attempt is made to pull the image.
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{{< note >}}
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To make sure the container always uses the same version of the image, you can specify its [digest](https://docs.docker.com/engine/reference/commandline/pull/#pull-an-image-by-digest-immutable-identifier); replace `<image-name>:<tag>` with `<image-name>@<digest>` (for example, `image@sha256:45b23dee08af5e43a7fea6c4cf9c25ccf269ee113168c19722f87876677c5cb2`). The digest uniquely identifies a specific version of the image, so it is never updated by Kubernetes unless you change the digest value.
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{{< /note >}}
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{{< note >}}
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You should avoid using the `:latest` tag when deploying containers in production as it is harder to track which version of the image is running and more difficult to roll back properly.
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{{< /note >}}
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{{< note >}}
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The caching semantics of the underlying image provider make even `imagePullPolicy: Always` efficient, as long as the registry is reliably accessible. With Docker, for example, if the image already exists, the pull attempt is fast because all image layers are cached and no image download is needed.
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{{< /note >}}
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## Using kubectl
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- Use `kubectl apply -f <directory>`. This looks for Kubernetes configuration in all `.yaml`, `.yml`, and `.json` files in `<directory>` and passes it to `apply`.
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- Use label selectors for `get` and `delete` operations instead of specific object names. See the sections on [label selectors](/docs/concepts/overview/working-with-objects/labels/#label-selectors) and [using labels effectively](/docs/concepts/cluster-administration/manage-deployment/#using-labels-effectively).
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- Use `kubectl create deployment` and `kubectl expose` to quickly create single-container Deployments and Services. See [Use a Service to Access an Application in a Cluster](/docs/tasks/access-application-cluster/service-access-application-cluster/) for an example.
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