feat(statefulset): improve the readme (#31)
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# Other topics
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# Stateful Sets
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## Introduction
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## Introduction
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In this section you will get an overview of others Kubernetes useful features, in order of complexity.
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Like a `Deployment`, a `StatefulSet` manages Pods that are based on an identical container spec. Unlike a `Deployment`, a `StatefulSet` maintains a sticky identity for each the pods. These are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.
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## Namespace
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`Namespaces` is the way to support multiple virtual clusters in Kubernetes.
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They are intended for use in environments with many users spread across multiple teams, or projects. For clusters with a few to tens of users, you should not need to create or think about `namespaces` at all. Start using `namespaces` when you need the features they provide.
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By default, all objects are in the `default` namespace. There is a "hidden" `namespace` where Kubernetes runs services for itself.
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Try:
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```sh
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$ kubectl get namespace
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NAME STATUS AGE
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default Active 56d
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kube-public Active 56d
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kube-system Active 56d
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```
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```sh
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$ kubectl get all --namespace=kube-system
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[lot of stuff]
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```
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## `kubeval`
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It is a tool to validate your Kubernetes YAML files: <https://github.com/garethr/kubeval>
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The easiest integration is with `docker run`, if you files are in the directory `kubernetes`
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```sh
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docker run -it -v `pwd`/kubernetes:/kubernetes garethr/kubeval kubernetes/**/*
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```
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## Helm
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It is a package manager for Kubernetes: <https://helm.sh/>.
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It contains multiple, ready to use, Kubernetes manifest for projects, for example [mysql](https://github.com/helm/charts/tree/master/stable/mysql)
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## Stateful Set
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Like a `Deployment`, a `StatefulSet` manages Pods that are based on an identical container spec. Unlike a `Deployment`, a `StatefulSet` maintains a sticky identity for each of their Pods. These pods are created from the same spec, but are not interchangeable: each has a persistent identifier that it maintains across any rescheduling.
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`StatefulSets` are valuable for applications that require one or more of the following.
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`StatefulSets` are valuable for applications that require one or more of the following.
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@ -88,10 +46,19 @@ spec:
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storage: 1Gi
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storage: 1Gi
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```
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```
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As you can see the manifest is very close to the one of a deployment. Apply the manigest [01-statefulset.yml](./01-statefulset.yml).
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Look at the pods generated, see how they are generated. Connect to one of the pods:
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```sh
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kubectl exec -ti web-0 /bin/bash
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```
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Write a file in the volume `www`. Terminate the same pod. See what happens. Reconnect to the pod, look at volume `www`. What can you see?
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## Exercises
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## Exercises
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1. Install `helm`, and use it to install [`redis`](https://github.com/helm/charts/tree/master/stable/redis) in your minikube
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Nothing to see here.
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2. Configure a stateful set for nginx with a HPA at 1% CPU, in a namespace `staging`
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## Clean up
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## Clean up
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