feat: add section on volumes

10-volumes/01-simple-mysql-pv.yml

@@ -0,0 +1,11 @@
+apiVersion: v1
+kind: PersistentVolume
+metadata:
+  name: mysql-pv-volume
+spec:
+  capacity:
+    storage: 1Gi
+  accessModes:
+    - ReadWriteOnce
+  hostPath:
+    path: "/mnt/data"

10-volumes/02-simple-mysql-pvc.yml

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+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: mysql-pv-claim
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 1Gi

10-volumes/03-simple-mysql-deployment.yml

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+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: mysql
+spec:
+  selector:
+    matchLabels:
+      app: mysql
+  strategy:
+    type: Recreate
+  template:
+    metadata:
+      labels:
+        app: mysql
+    spec:
+      containers:
+      - image: mysql:5.6
+        name: mysql
+        env:
+        - name: MYSQL_ROOT_PASSWORD
+          value: password
+        ports:
+        - containerPort: 3306
+          name: mysql
+        volumeMounts:
+        - name: mysql-persistent-storage
+          mountPath: /var/lib/mysql
+      volumes:
+      - name: mysql-persistent-storage
+        persistentVolumeClaim:
+          claimName: mysql-pv-claim

10-volumes/04-simple-mysql-service.yml

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+apiVersion: v1
+kind: Service
+metadata:
+  name: mysql
+spec:
+  ports:
+  - port: 3306
+  selector:
+    app: mysql
+  clusterIP: None

10-volumes/README.md

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+# Running a stateful application: `volumes`
+
+## Introduction
+
+In this section you will learn how to deploy a stateful application, mysql in this example.
+
+As you know a `pod` is mortal, meaning it can be destroyed by k8s anytime, and with it it's local data, memory, etc. So it's perfect for stateless applications. Of course, in the real world we need a way to store our data, and we need this data to be persistent in time.
+
+So how can we deploy a stateful application with a persistent storage in k8s? Let's deploy a mysql.
+
+## Volumes
+
+We need to review what a volume is before continuing with the deployment of our mysql. As stated above, the disk of a pod is destroyed with it, so it's lost. For a database it'll nice if we could keep the data between restarts of the pods. Here comes the `volume`.
+
+We can see a `pod` as something that requests CPU & RAM. We can see a `volume` as something that requests a storage on disk. K8s handles a lot of different kind of volumes - 26 has this file hands on is written - from local disk storage to s3.
+
+Here we will use `persistentVolumeClaim`, it's an abstraction over the hard drives of the k8s nodes - a fancy name for local hard drive.
+
+Let's create the volume where our mysql data will be stored.
+
+First we create the `PersistentVolume`. Ir is a piece of storage in the cluster that has been provisioned by a cluster administrator. It is a resource in the cluster just like a node is a cluster resource.
+
+```yaml
+apiVersion: v1
+kind: PersistentVolume
+metadata:
+  name: mysql-pv-volume
+spec:
+  capacity:
+    storage: 1Gi
+  accessModes:
+    - ReadWriteOnce
+  hostPath:
+    path: "/mnt/data"
+```
+
+Let's review some parameters:
+
+* `capacity`: the capacity of the volume
+  * `storage`: the volume size - here `1Gb`
+* `accessModes`: how this volume will be accessed, here `ReadWriteOnce`
+  * `ReadWriteOnce`: the volume can be mounted as read-write by a single node
+  * `ReadOnlyMany`: the volume can be mounted read-only by many nodes
+  * `ReadWriteMany`: the volume can be mounted as read-write by many nodes
+* `hostPath`: where the storage will be stored on the host, here `/mnt/data/`
+
+Apply it:
+
+```bash
+kubectl apply -f 10-volumes/01-simple-mysql-pv.yml
+```
+
+Now that we have a storage, we need to claim it, make it available for our pods. So we need a `PersistentVolumeClaim`. It is a request for storage by a user. It is similar to a pod. Pods consume node resources and `PersistentVolumeClaim` consume `PersistentVolume` resources.
+
+```yml
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: mysql-pv-claim
+spec:
+  accessModes:
+    - ReadWriteOnce
+  resources:
+    requests:
+      storage: 1Gi
+```
+
+The manifest is pretty similar to the `PersistentVolume`:
+
+```bash
+kubectl apply -f 10-volumes/02-simple-mysql-pvc.yml
+```
+
+## Stateful application
+
+Now let's create the `deployment` of mysql:
+
+```bash
+kubectl apply -f 10-volumes/03-simple-mysql-deployment.yml
+```
+
+There is a bunch of parameters we haven't seen yet:
+
+* `strategy`: the strategy of updates of the pods
+  * `type`: `Recreate`. This instructs Kubernetes to not use rolling updates. Rolling updates will not work, as you cannot have more than one Pod running at a time.
+* `env`: the list of environment variables to pass to the container
+  * `name`: the name of the env variable
+  * `value`: the value of the env variable
+* `volumeMounts`: the volumes, think directories, to give access to the container
+  * `name`: the name of the volume to mount
+  * `mountPath`: where in the container to mount the volume
+* `volumes`: the volumes to request access to
+  * `name`: the name of the volume, same as `volumeMounts.name`
+  * `persistentVolumeClaim`: the `PersistentVolumeClaim` we want
+    * `claimName`: the name of the claim
+
+Let's finish by creating a `service` to have stable DNS entry inside our cluster.
+
+```bash
+kubectl apply -f 10-volumes/04-simple-mysql-service.yml
+```
+
+Finally let's access the mysql
+
+```bash
+kubectl run -it --rm --image=mysql:5.6 --restart=Never mysql-client -- mysql -h mysql -ppassword
+
+If you don't see a command prompt, try pressing enter.
+
+mysql> show databases;
++--------------------+
+| Database           |
++--------------------+
+| information_schema |
+| mysql              |
+| performance_schema |
++--------------------+
+3 rows in set (0.02 sec)
+```
+
+Create a new database in mysql:
+
+```bash
+mysql> CREATE DATABASE testing;
+Query OK, 1 row affected (0.01 sec)
+```
+
+Now delete the service and the deployment:
+
+```bash
+kubectl delete service,deployment --all
+```
+
+Recreate them, reconnect to mysql and see if you still have the database `testing` you created.
+
+## Exercices
+
+Nothing to see here.
+
+## Clean up
+
+```bash
+kubectl delete service,deployment,pvc,pv,pod --all
+```