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Kubernetes Notes



Kubernetes cheatsheet and notes, wrote while learning and working on k8s related projects.

Table of Contents:

Basic Terms

some basic termnologies used by kubernetes
  1. cluster: physical cluster of physical machine.
  2. context: a group of access parameters, a cluster, a namespace, a user.
  3. namespace: virtual cluster, use to separate resources across different environments like prod, dev, test.
  4. node: a virtual/physical machine
  5. pod: a set of containers to orchestrate, minimal object to scale
  6. container: docker container runs in pod
  7. chart: a collect of files that describes your pod orchestration, that can be used to deploy a set of pods.
  8. Job: a wrapper to pod, usually runs a pod that carrying tasks that run only once, like db migration.
  9. Service: a wrapper to pod, one or more pods to perform a service.
  10. Volumes: file storage system, lives with node. Can define external volumes on cloud providers, lives with cloud providers.
  11. Label: to classify different kind of pods.


Manifests

manifests usually defined by .yaml or .json file, to manage (describe) resources.

- Deployment: deploy pods based on spec
- ReplicaSet: deploy pods as replica 
- DaemonSet:  deploy pods based on spec, ensure each node get one replica.
- HorizontalPodsAutoscaler(HPA): Autoscaler for pods, make sure the resources usage keeps at same level.(50% CPU/Memory Usage)
- Volume Claim Chain: To better manage a externel volume, to use a volume, must first claim it.
- Network Policy: Define a network policy to a set of pods(by label) like which set of pods(by label) or users(by namespace) can access.
- Secret: some secret you don't want others to know: ssh key, username/password
- Ingress:

Expose A Service

  1. Create a Kind:Service yaml, and define which pods your service is using (by using label)

There are 3 types of manifests to expose a service

  1. NodePort: Assign the service to a port, access the service by port number. Ex:<NodeIP>:<PortNumber>, PortNumber is fixed, NodeIP could be any node that the service is running on. pods traffic is balanced in the same node, but not balanced in the different nodes . This is not good for production, but good for local testing by using kube-proxy.

  2. LoadBalancer: Similar to NodePort, but expose the all <NodeIP>:<PortNumber>=to a external load balancer. Node traffic is balanced.

  3. Ingress: Recommended way for production.

Tools

kubectl, kubeadmin, minikube, helm

  1. Kubectl

    Kubectl is a user tool to interact with the cluster

    1. get info about the cluster (pod, service, deployment, replicaset, statefulset etc):

      everything: kubectl get all
      pods: kubectl get pods
      nodes:kubectl get nodes
      Note: can be filtered by namespace or label.

    2. get logs for a pod:

      usage: kubectl logs -h

    3. forward a request from a port:

      usage: kubectl port-forward -h

  2. Helm

    Helm is like a manager of charts, you can use helm to pull, push, deploy a chart and modify (upgrade) a depolyment.

    1. pull repo from remote chart repository to local:

      helm repo add [repoName] [RepoUrl]
      helm update

    2. deploy (install) chart from local repo:

      helm install [repoName]/[chartName] [releaseName]
      [releaseName] can be auto-generated using --generate-name

    3. upgrade:

      – get values.yaml of a chart, stores at values.yaml
      helm inspect values [chartName] > newValues.yaml
      – edit the newValues.yaml to describe the upgrade
      – deploy the upgrade
      helm upgrade [releaseName] [chartName] -f newValues.yaml

    4. clean/remove the release:

      helm uninstall [releaseName]

  3. Kubeadm

    Kubeadm is admin tool to setup a cluster







  4. Minikube

    Minikube: setup & run a single node cluster locally for testing and dev purpose.

    1. usage: minikube -h
    2. usual workflow:

      minikube start [computingResourceConfig]
      minikube status
      minikube stop

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