Kubernetes-learning

Learning Kubernetes through experimentation.

Setup

I'm working on Windows, I have multiple minor issues when I try several things with minikube and docker, so I will work into the WSL2 environment.

Docker Desktop for Windows allows to use it from within WSL2. I clone my repository within the WSL2 environment to dodge any further Windows Linux conflicts.

    cd ~/repositories/
    git clone <github project>

Install minikube and kubectl within WSL2

Follow these steps to install the required tools.

First step - simple mongodb environment application without persistent volume

Branch simple-mongodb-deployment

The goal here is to learn to deploy the following :

• Mongodb
• Mongo-express (web-application)

We won't use Helm charts.

Architecture

We don't want the mongodb to be publicly reachable, so we will expose it only within the k8s cluster.

We will access the mongodb only through mongo-express, so it will be publicly reachable.

We will not set a Persistent Volume (PV).

Steps

• Launch Docker Desktop on Windows
• minikube start
• Create the mongodb deployment
• Create the secret
• Apply the secret
• Reference values from the secret into the mongodb deployment
• Apply the deployment
• Create the mongodb service (internal, ClusterIP) in the same file as the deployment
• Create the ConfigMap (contain the mongodb server address) and apply it
• Create the mongo-express deployment and apply it
• Create the mongo-express LoadBalancer service in the same file and reapply it
• Run minikube service mongo-express-service

Second step - add a persistent volume

Branch persistent-volume

The goal is to learn how to add a persistent volume.

Steps

• Create a Persistent Volume (local for learning, in production I would use a StorageClass)
• Turn "Headless" the mongodb service (needed for StatefulSets to allow stable network identities)
• Replace the mongodb Deployment with a StatefulSet
• kubectl apply -f config-map.yaml
• kubectl apply -f secret.yaml
• kubectl apply -f persistent-volume.yaml
• kubectl apply -f mongodb-stateful.yaml
• kubectl apply -f mongo-express.yaml
• kubectl get pods --watch
• minikube service mongo-express-service

We don't need a PVC because the StatefulSet handle it with its volumeClaimTemplates.

Test the persistency

• Go on mongo-express to create a database
• kubectl delete pod mongodb-statefulset-0 : k8s delete the pod and recreate it automatically.
• Once the pod is recreated and running, return to mongo-express and check that the created database is still present.