Kubernetes Tutorial

Using this tutorial to learn Kubernetes concepts: https://www.youtube.com/watch?v=X48VuDVv0do. minikube needs to run in a virtual environment, so we need to specify the vm-driver, hypberkit in our case.

minikube start --vm-driver=hyperkit

Once minikube is set up, it spins up a VM and then you can use kubectl to query it. Minikube is a node, running virtually in your own computer.

Basic Commands Usage

creat a pod: kubectl create .... We don’t notmally work with pods directly. We work with deployments. So we use kubectl create deploymend NAME --image=image. The image needs to be specified since the pod needs to be created using some image

The deployment contains the blueprint for the pods. So it tells Kub what to create in the pod

kubectl get replicaset shows us the status of the pods replicas

• Deployment manages a
• replicaset manages a
• pod is an abstractin of the
• container

we only worry about deployments. Kubernetes handles everything below thato

Debugging

kubectl logs NAME_OF_POD (get the name from kubectl get pods)

kubectl exec -it NAME_OF_POD -- bin/bash will open a bash terminal in the pod (-it means interactive terminal)

Configuration Files

In practice you use a configuration file

kubectl apply -f config-file.yaml

Kubernetes will attempt to make the deployment match the configuration file

file

apiVersion: kind: Deployment metadata: name: labels: spec: replicas: selector: template: this part is for the pods metadata: … spec:

[status] automatically generated by kuberenetes Kubernetes compares the status with the specs to make sure everything is where it needs to be

.yaml is very strict about indentations FYI

normally stored with the code.

labels must match app so that the service can know which pods it is managing

Example

internal service configMap with DB url secret with DB user and DB pwd

mongo-express will be available via an external service

mongo-express web app -> mongo express external service -> mongo express pod -> mongoDB internal service -> mongoDB pod 2 deployment/pod

when we set up the configuration file, we need some passwords and usernames, which we DON’T want to expose So we store them in a secret.yaml file.

To store them, we should encrypt them as base64, and to do that echo -n 'mystring' | base64

Once you configure the secret, you actually have to apply it so it exists when you refer it

now we create an internal service so that other pods can talk to this pod

the selector of the service needs to match the label of the deployment

now we create the mongoexpress deployment. Needs to know which MongoDB (address internal service) and credentials found in the docker image page

remember to create the configmap before you try to access it (creating it means running kubectl apply -f the-configmap.yaml)

Once we have the express pod running, we can then set up the external service, so that a browser can connect to the web app from external to the cluster

How to make an external service: needs to have type LoadBalancer (but internal service also has this type, but we need to write it here) it assigns the service an external IP address also specify a nodePort

to actually get the external IP for a minikube setup, we need to run minikube service name-of-service