From c76108af04ecbfc4e8de0e407016379e01698e0d Mon Sep 17 00:00:00 2001
From: Michele Cereda <cereda.michele@gmail.com>
Date: Sun, 16 Jul 2023 22:40:55 +0200
Subject: [PATCH] chore: improved readibility

---
 ...eck a pod can connect to an external db.md | 35 ----------------
 .../check pods can connect to external dbs.md | 40 +++++++++++++++++++
 .../{drain a node.md => drain nodes.md}       | 13 +++---
 knowledge base/kubernetes/helm.md             | 39 +++++++++++-------
 4 files changed, 72 insertions(+), 55 deletions(-)
 delete mode 100644 knowledge base/kubernetes/check a pod can connect to an external db.md
 create mode 100644 knowledge base/kubernetes/check pods can connect to external dbs.md
 rename knowledge base/kubernetes/{drain a node.md => drain nodes.md} (76%)

diff --git a/knowledge base/kubernetes/check a pod can connect to an external db.md b/knowledge base/kubernetes/check a pod can connect to an external db.md
deleted file mode 100644
index 20fa22e..0000000
--- a/knowledge base/kubernetes/check a pod can connect to an external db.md	
+++ /dev/null
@@ -1,35 +0,0 @@
-# Check a Pod can connect to an external DB
-
-## Table of contents <!-- omit in toc -->
-
-1. [TL;DR](#tldr)
-1. [Further readings](#further-readings)
-
-## TL;DR
-
-```sh
-# access a test container
-kubectl run --generator=run-pod/v1 --limits 'cpu=200m,memory=512Mi' --requests 'cpu=200m,memory=512Mi' --image alpine ${USER}-mysql-test -it -- sh
-
-# install programs
-apk --no-cache add mysql-client netcat-openbsd
-
-# test plain connectivity
-nc -vz -w3 10.0.2.15 3306
-
-# test the client can connect
-mysql --host 10.0.2.15 --port 3306 --user root
-```
-
-## Further readings
-
-- [Kubernetes]
-- [`kubectl`][kubectl]
-
-<!--
-  References
-  -->
-
-<!-- Knowledge base -->
-[kubectl]: kubectl.md
-[kubernetes]: README.md
diff --git a/knowledge base/kubernetes/check pods can connect to external dbs.md b/knowledge base/kubernetes/check pods can connect to external dbs.md
new file mode 100644
index 0000000..2b9cdad
--- /dev/null
+++ b/knowledge base/kubernetes/check pods can connect to external dbs.md	
@@ -0,0 +1,40 @@
+# Check Pods can connect to external DBs
+
+## Table of contents <!-- omit in toc -->
+
+1. [TL;DR](#tldr)
+1. [Further readings](#further-readings)
+
+## TL;DR
+
+1. Get a shell on a test container.
+   ```sh
+   kubectl run --generator='run-pod/v1' --image 'alpine' -it --rm \
+     --limits 'cpu=200m,memory=512Mi' --requests 'cpu=200m,memory=512Mi' \
+     ${USER}-mysql-test -- sh
+   ```
+1. Install the utility applications needed for the tests.
+   ```sh
+   apk --no-cache add 'mysql-client' 'netcat-openbsd''
+   ```
+1. Test basic connectivity to the external service.
+   ```sh
+   nc -vz -w3 '10.0.2.15' '3306'
+   ```
+1. Test application connectivity.
+   ```sh
+   mysql --host '10.0.2.15' --port '3306' --user 'root'
+   ```
+
+## Further readings
+
+- [Kubernetes]
+- [`kubectl`][kubectl]
+
+<!--
+  References
+  -->
+
+<!-- Knowledge base -->
+[kubectl]: kubectl.md
+[kubernetes]: README.md
diff --git a/knowledge base/kubernetes/drain a node.md b/knowledge base/kubernetes/drain nodes.md
similarity index 76%
rename from knowledge base/kubernetes/drain a node.md
rename to knowledge base/kubernetes/drain nodes.md
index 2caf36d..36345ce 100644
--- a/knowledge base/kubernetes/drain a node.md	
+++ b/knowledge base/kubernetes/drain nodes.md	
@@ -1,4 +1,4 @@
-# Drain a K8S cluster node
+# Drain nodes in K8S clusters
 
 ## Table of contents <!-- omit in toc -->
 
@@ -8,14 +8,16 @@
 
 ## TL;DR
 
-1. mark the node as unschedulable (_cordon_):
+1. **Cordon** the Nodes.<br/>
+   This marks each Node as _unschedulable_ and prevents new Pods to start on them.
 
    ```sh
    $ kubectl cordon 'kworker-rj2'
    node/kworker-rj2 cordoned
    ```
 
-1. remove pods running on the node:
+1. **Drain** the nodes.<br/>
+   This _evicts_ Pods already running on the Nodes.
 
    ```sh
    $ kubectl drain 'kworker-rj2' --grace-period=300 --ignore-daemonsets=true
@@ -26,8 +28,9 @@
    node/kworker-rj2 evicted
    ```
 
-1. do to the node what you need to do
-1. make the node available again:
+1. Do to the Nodes what you need to do.
+1. **Uncordon** the Nodes.
+   This makes them available for scheduling again.
 
    ```sh
    $ kubectl uncordon 'kworker-rj2'
diff --git a/knowledge base/kubernetes/helm.md b/knowledge base/kubernetes/helm.md
index 5f780e8..1ee6026 100644
--- a/knowledge base/kubernetes/helm.md	
+++ b/knowledge base/kubernetes/helm.md	
@@ -16,26 +16,34 @@ helm plugin list
 helm plugin ls
 
 # Install new plugins.
-helm plugin add https://github.com/author/plugin
-helm plugin install path/to/plugin
+helm plugin add 'https://github.com/author/plugin'
+helm plugin install 'path/to/plugin'
 
 # Update installed plugins.
-helm plugin update plugin-name
-helm plugin up plugin-name
+helm plugin update 'plugin_name'
+helm plugin up 'plugin_name'
 
 # Uninstall plugins.
-helm plugin rm plugin-name
-helm plugin remove plugin-name
-helm plugin uninstall plugin-name
+helm plugin rm 'plugin_name'
+helm plugin remove 'plugin_name'
+helm plugin uninstall 'plugin_name'
 
-# Manage repositories.
+
+# List added repositories.
 helm repo list
+
+# Add repositories.
 helm repo add 'grafana' 'https://grafana.github.io/helm-charts'
 helm repo add 'ingress-nginx' 'https://kubernetes.github.io/ingress-nginx'
+
+# Update repositories.
 helm repo update
 helm repo update 'keda'
+
+# Remove repositories.
 helm repo remove 'prometheus'
 
+
 # Search for specific charts
 helm search hub --max-col-width '100' 'ingress-nginx'
 helm search repo 'grafana'
@@ -50,6 +58,7 @@ helm pull 'ingress-nginx/ingress-nginx' --version '4.0.6' \
 # Get the default values of specific charts.
 helm inspect values 'gitlab/gitlab'
 
+
 # Install releases
 helm install 'my-gitlab' 'gitlab/gitlab'
 helm upgrade --install 'my-gitlab' 'gitlab/gitlab'
@@ -61,13 +70,13 @@ helm upgrade --install 'keda' 'keda' \
   --repo 'https://kedacore.github.io/charts' \
   --namespace 'keda' --create-namespace
 
-# Upgrade deployed releases
+# Upgrade deployed releases.
 helm upgrade --install 'my-wordpress' 'wordpress'
-helm upgrade --values values.yaml 'my-wordpress' 'wordpress'
+helm upgrade --values 'values.yaml' 'my-wordpress' 'wordpress'
 helm upgrade --namespace 'gitlab' --values 'values.yaml' 'gitlab gitlab/gitlab' --dry-run
 helm upgrade --atomic --create-namespace --namespace 'gitlab' --timeout 0 --values 'values.yaml' 'gitlab' 'gitlab/gitlab' --debug
 
-# Inspect deployed releases' manifest
+# Inspect deployed releases' manifests.
 helm get manifest 'wordpress'
 ```
 
@@ -82,12 +91,12 @@ To achieve this:
    ```yaml
    annotations:
      meta.helm.sh/release-name: app-release-name
-     meta.helm.sh/release-namespace: app-deploy-namespace-name
+     meta.helm.sh/release-namespace: app-deployment-namespace-name
    labels:
      app.kubernetes.io/managed-by: Helm
    ```
 
-   with `app-release-name` being the release name used to deploy the helm chart and `app-deploy-namespace-name` being the deployment namespace
+   with `app-release-name` being the release name used to deploy the helm chart and `app-deployment-namespace-name` being the deployment namespace.
 
    ```sh
    kubectl annotate "$KIND" "$NAME" "meta.helm.sh/release-name=${RELEASE_NAME}"
@@ -95,11 +104,11 @@ To achieve this:
    kubectl label "$KIND" "$NAME" "app.kubernetes.io/managed-by=Helm"
    ```
 
-1. add now the existing resources' manifests to the chart
+1. now, add the existing resources' manifests to the chart
 1. execute a chart upgrade:
 
    ```sh
-   helm upgrade <app-release-name>
+   helm upgrade 'app-release-name'
    ```
 
 ## Further readings