Kubernetes

Notes

• k is an alias setup in my .zshrc for kubectl

• kubectl services $SERVICENAME --url can be used to get the ip and endpoint of a service

Namespaces

• Namespace is a logical grouping of resources. It isolates groups in a cluster

• Creating new namespaces can be done by k create namespace ${nameSpaceName}

• Deleting a namespace can be done by k delete namespace ${nameSpaceName} it also deletes the resources inside, so for testing it's always a great practice to create a test namespace and later on delete it

• Setting a namespace as current one (equivalent of USE DATABASE in SQL) can be done by: k config set-context --current --namespace=${nameOfExistingNamespace}

Pods

• Good way of explaining it to students: Operating System of the cloud

• For generating a barebone yaml for a pod, the fastest way is: k run nginx-yaml --image=nginx --dry-run=client -o yaml > nginx.yaml

• To delete pods, we can use: k delete pod ${nameOfPod}

• To get into the pod we use: k exec -it ${nameOfPod} -- /bin/bash, same as docker containers

• Strategy RollingUpdate is the default, it's the strategy which waits for the update and then removes the old pods

• If there is no -n attribute refering to the namespace, the pod gets run in default automatically

• Port forwarding can be done with k port-forward ${podName} ${portNumber}

Networking

• Kubernetes achieves pods seeing each other through the usage of a CNI plugin, which is a Container Networking Interface

• Most used CNI plugins are:

  • Cilium

  • Calico

  • Flannel

Services

• A service is a grouping of Pods

• The missing step between pods and services is generating a deployment, it can be done by doing: k create deployment ${nameOfDeployment} --image=nginx --dry-run=client -o yaml > deployment.yaml and then changing the ports and the image

• k expose generates a service by itself

• A yaml description can be generated by running: k get services ${nameOfService} -o yaml > service.yaml command for a running service.

• The easiest way to make a service accesible on an externalIP is by generating a yaml for it and chaning the type of it to: type:LoadBalancer which is going to expose the service on an externalIP while also keeping it running so you don't need to port-forward it, which has to be put in the background in order not to get cancelled

• In Rancher the externalIP works only if the preferences has the administrative rights ticked in

Note to Self

• Do a raw deployment, change image and ports. Apply, it runs it as a svc, then generate service description, change type to LoadBalancer -> apply -> get access on externalIP

Links