fix(k8s): set affinity examples for addons

knowledge base/kubernetes/cluster autoscaler.md

@@ -1,18 +1,25 @@
 # Cluster autoscaler
 
-Automatically adjusts the number of nodes in Kubernetes clusters.
+Automatically adjusts the number of nodes in Kubernetes clusters to meet their current needs.
 
 1. [TL;DR](#tldr)
+1. [Best practices](#best-practices)
 1. [Further readings](#further-readings)
    1. [Sources](#sources)
 
 ## TL;DR
 
-Acts when one of the following conditions is true:
+The purpose of Cluster Autoscaler is to get pending pods a place to run on.
 
-- Pods failed to run in the cluster due to insufficient resources.
-- Nodes in the cluster have been underutilized for an extended period of time, and their pods can be placed on other
-  existing nodes.
+The autoscaler acts when one of the following conditions is true:
+
+- Pods failed to run in the cluster due to insufficient resources.<br/>
+  This triggers a scale-**up** event, where it will try to **add** a new node.
+- Nodes in the cluster have been consistently underutilized for a significant amount of time, and their pods can be
+  moved on other existing nodes.<br/>
+  This triggers a scale-**down** event, where it will try to **remove** an existing node.
+
+The time required for node provisioning depends on the cloud provider and other Kubernetes components.
 
 <details>
   <summary>Setup</summary>
@@ -31,27 +38,36 @@ helm --namespace 'kube-system' uninstall 'cluster-autoscaler'
 
 </details>
 
-<!-- Uncomment if used
-<details>
-  <summary>Usage</summary>
-
-```sh
-```
-
-</details>
--->
-
 <details>
   <summary>Real world use cases</summary>
 
 ```sh
-helm --namespace 'kube-system' upgrade --install 'cluster-autoscaler' 'autoscaler/cluster-autoscaler' \
-  --set 'cloudProvider'='aws' --set 'awsRegion'='eu-west-1' \
-  --set 'autoDiscovery.clusterName'='defaultCluster' --set 'rbac.serviceAccount.name'='cluster-autoscaler-aws'
+aws eks --region 'eu-west-1' update-kubeconfig --name 'custom-eks-cluster' \
+&& helm --namespace 'kube-system' upgrade --install --repo 'https://kubernetes.github.io/autoscaler' \
+  'cluster-autoscaler' 'cluster-autoscaler' \
+  --set 'cloudProvider'='aws' --set 'awsRegion'='eu-west-1' --set 'autoDiscovery.clusterName'='custom-eks-cluster' \
+  --set 'rbac.serviceAccount.name'='cluster-autoscaler-aws' \
+  --set 'replicaCount'='2' \
+  --set 'resources.requests.cpu'='40m' --set 'resources.requests.memory'='50Mi' \
+  --set 'resources.limits.cpu'='100m' --set 'resources.limits.memory'='300Mi' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].weight'='100' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.topologyKey'='kubernetes.io/hostname' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.labelSelector.matchExpressions[0].key'='app.kubernetes.io/name' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.labelSelector.matchExpressions[0].operator'='In' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.labelSelector.matchExpressions[0].values[0]'='aws-cluster-autoscaler'
 ```
 
 </details>
 
+## Best practices
+
+- Do **not** modify nodes belonging to autoscaled node groups directly.
+- All nodes within the same autoscaled node group should have the same capacity, labels and system pods running on them.
+- Specify requests for all the pods one can.
+- Should one need to prevent pods from being deleted too abruptly, consider using PodDisruptionBudgets.
+- Check one's cloud provider's quota is big enough **before** specifying min/max settings for clusters' node pools.
+- Do **not** run **any** additional node group autoscaler (**especially** those from one's own cloud provider).
+
 ## Further readings
 
 - [Main repository]

knowledge base/kubernetes/metrics server.md

@@ -29,7 +29,14 @@ Depending on the metrics-server version it uses:
 ```sh
 kubectl apply -f 'https://github.com/kubernetes-sigs/metrics-server/releases/latest/download/components.yaml'
 helm -n 'kube-system' upgrade --install --repo 'https://kubernetes-sigs.github.io/metrics-server' \
-  'metrics-server' 'metrics-server' --set 'containerPort'='10251'
+  'metrics-server' 'metrics-server' \
+  --set 'replicas'='2' --set 'addonResizer.enabled'='true' \
+  --set 'containerPort'='10251' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].weight'='100' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.topologyKey'='kubernetes.io/hostname' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.labelSelector.matchExpressions[0].key'='app.kubernetes.io/name' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.labelSelector.matchExpressions[0].operator'='In' \
+  --set 'affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.labelSelector.matchExpressions[0].values[0]'='metrics-server'
 ```
 
 </details>