feat: add other topics (#30)

Author: ElPicador

98-other-topics/README.md

@@ -0,0 +1,57 @@
+# Other topics
+
+## Introduction
+
+In this section you will get an overview of others Kubernetes useful features, in order of complexity.
+
+## Namespace
+
+`Namespaces` is the way to support multiple virtual clusters in Kubernetes.
+
+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.
+
+By default, all objects are in the `default` namespace. There is a "hidden" `namespace` where Kubernetes runs services for itself.
+Try:
+
+```sh
+$ kubectl get namespace
+NAME          STATUS    AGE
+default       Active    56d
+kube-public   Active    56d
+kube-system   Active    56d
+```
+
+```sh
+$ kubectl get all --namespace=kube-system
+
+[lot of stuff]
+```
+
+## `kubeval`
+
+It is a tool to validate your Kubernetes YAML files: https://github.com/garethr/kubeval
+
+The easiest integration is with `docker run`, if you files are in the directory `kubernetes`
+
+```sh
+docker run -it -v `pwd`/kubernetes:/kubernetes garethr/kubeval kubernetes/**/*
+```
+
+## Helm
+
+It is a package manager for Kubernetes: https://helm.sh/.
+It contains multiple, ready to use, Kubernetes manifest for projects, for example [mysql](https://github.com/helm/charts/tree/master/stable/mysql)
+
+## Kube state metrics
+
+[Kube State Metrics](https://github.com/kubernetes/kube-state-metrics) is a service you can install on your Kubernetes clusters to get metrics from its state. It's very useful for production cluster as you can measure and put alerts on the state of your applications. Like when do you have pod evictions, are your deployment fully deployed, etc.
+
+## Exercises
+
+Nothing to see here.
+
+## Clean up
+
+```sh
+kubectl delete statefulset,deployment,service,pod --all
+```

README.md

@@ -21,6 +21,7 @@
 1. [Controllers: what, why, and how](#controllers-what,-why,-and-how)
 1. [Operators and CRDs: what, why, and how](#operators-and-crds-what,-why,-and-how)
 1. [RBAC](#rbac)
+1. [Other topics](#other-topics)
 1. [Good practices](#good-practices)
 1. [Links](#links)
 
@@ -255,6 +256,10 @@ See the dedicated [README](20-operators).
 
 See the dedicated [README](21-rbac).
 
+## Other topics
+
+See the dedicated [README](98-other-topics).
+
 ## Good practices
 
 See the dedicated [README](99-good-practices).