Kubernetes

Frequently used code for kubernetes

Recipes

Installing kubectl

(dependencies):

sudo apt-get update && sudo apt-get install -y apt-transport-https gnupg2

sudo curl -fsSLo /usr/share/keyrings/kubernetes-archive-keyring.gpg https://packages.cloud.google.com/apt/doc/apt-key.gpg

echo "deb [signed-by=/usr/share/keyrings/kubernetes-archive-keyring.gpg] https://apt.kubernetes.io/ kubernetes-xenial main" | sudo tee /etc/apt/sources.list.d/kubernetes.list

sudo apt-get update
sudo apt-get install -y kubectl

Check version

kubectl version --client

Installing minikube

curl -LO https://storage.googleapis.com/minikube/releases/latest/minikube_latest_amd64.deb
sudo dpkg -i minikube_latest_amd64.deb

Installing KVM

sudo apt-get install qemu-kvm libvirt-daemon-system libvirt-clients bridge-utils

Installing helm

curl https://baltocdn.com/helm/signing.asc | sudo apt-key add -
sudo apt-get install apt-transport-https --yes
echo "deb https://baltocdn.com/helm/stable/debian/ all main" | sudo tee /etc/apt/sources.list.d/helm-stable-debian.list
sudo apt-get update
sudo apt-get install helm

Start cluster

minikube start

Disconnect from remote cluster

kubectl config use-context minikube

Delete namespace

kubectl delete namespace <name-of-the-namespace>

Create namespace

kubectl create namespace twitter-executor

To run a service from minikube

minikube service <name-of-the-service> -n <name-of-the-namespace>

for example for jupyterhub: minikube service proxy-public -n jhub

To inspect running cluster

minikube dashboard

Applying conf changes

Change config.yaml

Execute helm upgrade as follows:

# In some cases to guarantee upgrade:
# These two need to be run every time config.yaml is updated it
# helm repo add jupyterhub https://jupyterhub.github.io/helm-chart/
# helm repo update
RELEASE=jhub
NAMESPACE=jhub
helm upgrade --cleanup-on-fail \
  $RELEASE jupyterhub/jupyterhub \
  --namespace $NAMESPACE \
  --version=0.10.6 \
  --values config.yaml # --timeout 2000s if internet slow

Verify hub and proxy pods:

NAMESPACE=jhub
kubectl get pod --namespace $NAMESPACE

Set new image for a given deployment

kubectl set image deploy DEPLOYMENT_NAME IMAGENAME=IMAGENAME:ERSION

Get revisions

kubectl get rs -n NAMESPACE

Rollback to previous revision

kubectl rollout undo deployment DEPLOYMENT_NAME --to-revision=REVISION_NUMBER

Inspect revisions

kubectl rollout history deploy DEPLOYNAME -n NAMESPACE --revision=REVISION_NUMBER

Revisions used for rollback are available as their new revision instead of their original.

Access a pod shell

kubectl exec --stdin --tty POD_NAME -- /bin/bash

Restart a deployment

kubectl rollout restart deployments/DEPLOYMENT_NAME

That's what the selector field in the service manifest is for

Scale deployment

kubectl scale deployment tasksapp --replicas=3

Set namespace

kubectl config set-context --current --namespace=dev

Services

Connection

Environment Variables As soon as the Pod starts on any worker node, the kubelet daemon running on that node adds a set of environment variables in the Pod for all active Services. For example, if we have an active Service called redis-master, which exposes port 6379, and its ClusterIP is 172.17.0.6, then, on a newly created Pod, we can see the following environment variables:
*REDIS_MASTER_SERVICE_HOST=172.17.0.6* *REDIS_MASTER_SERVICE_PORT=6379* *REDIS_MASTER_PORT=tcp://172.17.0.6:6379* *REDIS_MASTER_PORT_6379_TCP=tcp://172.17.0.6:6379* *REDIS_MASTER_PORT_6379_TCP_PROTO=tcp* *REDIS_MASTER_PORT_6379_TCP_PORT=6379* *REDIS_MASTER_PORT_6379_TCP_ADDR=172.17.0.6*
With this solution, we need to be careful while ordering our Services, as the Pods will not have the environment variables set for Services which are created after the Pods are created.
DNS Kubernetes has an add-on for DNS, which creates a DNS record for each Service and its format is my-svc.my-namespace.svc.cluster.local. Services within the same Namespace find other Services just by their names. If we add a Service redis-master in *my-ns* Namespace, all Pods in the same my-ns Namespace lookup the Service just by its name, *redis-master*. Pods from other Namespaces, such as test-ns, lookup the same Service by adding the respective Namespace as a suffix, such as redis-master.my-ns or providing the FQDN of the service as redis-master.my-ns.svc.cluster.local. This is the most common and highly recommended solution. For example, in the previous section's image, we have seen that an internal DNS is configured, which maps our Services frontend-svc and *db-svc* to 172.17.0.4 and 172.17.0.5 IP addresses respectively.

ServiceType

ClusterIP is the default *ServiceType*. A Service receives a Virtual IP address, known as its ClusterIP. This Virtual IP address is used for communicating with the Service and is accessible only from within the cluster.

With the NodePort ServiceType, in addition to a ClusterIP, a high-port, dynamically picked from the default range 30000-32767, is mapped to the respective Service, from all the worker nodes. For example, if the mapped NodePort is 32233 for the service frontend-svc, then, if we connect to any worker node on port *32233*, the node would redirect all the traffic to the assigned ClusterIP - *172.17.0.4*. If we prefer a specific high-port number instead, then we can assign that high-port number to the NodePort from the default range when creating the Service.

The *NodePort* ServiceType is useful when we want to make our Services accessible from the external world. The end-user connects to any worker node on the specified high-port, which proxies the request internally to the ClusterIP of the Service, then the request is forwarded to the applications running inside the cluster. Let's not forget that the Service is load balancing such requests, and only forwards the request to one of the Pods running the desired application. To manage access to multiple application Services from the external world, administrators can configure a reverse proxy - an ingress, and define rules that target specific Services within the cluster.

LoadBalancer

NodePort and ClusterIP are automatically created, and the external load balancer will route to them
The Service is exposed at a static port on each worker node
The Service is exposed externally using the underlying cloud provider's load balancer feature.

The LoadBalancer ServiceType will only work if the underlying infrastructure supports the automatic creation of Load Balancers and have the respective support in Kubernetes, as is the case with the Google Cloud Platform and AWS. If no such feature is configured, the LoadBalancer IP address field is not populated, it remains in Pending state, but the Service will still work as a typical NodePort type Service.

Sample manifests

configMap

apiVersion: v1
kind: ConfigMap
metadata:
  name: dev-env # parameter
data:
  APP_ENV: "DEV"
# ...

secrets

apiVersion: v1
kind: Secret
metadata:
  name: dev-password # parameter
type: Opaque
stringData:
  APP_SECRET_KEY: XYZZ
# ...

**deployment **

apiVersion: apps/v1
kind: Deployment
metadata:
  name: IMAGE_NAME
  labels:
    app: IMAGE_NAME
spec:
  selector:
    matchLabels:
      app: IMAGE_NAME
  replicas: 1
  template:
    metadata:
      labels:
        app: IMAGE_NAME
    spec:
      containers:
      - name: IMAGE_NAME
        image: DOCKER_HUB_USER/IMAGE_NAME:IMAGE_TAG # This needs to change over deployments to ensure update
        imagePullPolicy: Always
        ports:
          - containerPort: 8080
        resources:
          requests:
            cpu: "250m"
        envFrom:
          - configMapRef:
              name: dev-env # ^ from configMap
        env:
        - name: APP_SECRET_KEY
          valueFrom:
            secretKeyRef:
              name: dev-password # ^ from secrets
              key: APP_SECRET_KEY

service

apiVersion: v1
kind: Service
metadata:
  name: IMAGE_NAME-service
spec:
  selector:
    app: IMAGE_NAME
  ports:
  - port: 80
    targetPort: 8080
  type: LoadBalancer

Storage

references

Resources

https://keda.sh/
https://www.bodyworkml.com/
https://github.com/CrunchyData/postgres-operator

References

https://kubernetes.io/docs/tasks/tools/install-minikube/
https://kubernetes.io/docs/tasks/tools/install-kubectl/#install-kubectl-on-linux
https://minikube.sigs.k8s.io/docs/start/
https://help.ubuntu.com/community/KVM/Installation#Installation
https://minikube.sigs.k8s.io/docs/handbook/accessing/#using-minikube-tunnel
https://levelup.gitconnected.com/deploy-your-first-flask-mongodb-app-on-kubernetes-8f5a33fa43b4
https://github.com/testdrivenio/flask-vue-kubernetes !! Useful
https://kubernetes.io/docs/concepts/services-networking/network-policies/
https://artifacthub.io/
https://github.com/helm/charts
https://kubernetes.io/docs/concepts/workloads/controllers/job/
https://kubernetes.io/docs/tasks/job/automated-tasks-with-cron-jobs/
https://kubernetes.io/docs/concepts/extend-kubernetes/api-extension/apiserver-aggregation/

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Last updated 3 years ago