Deploy an App

Deployments, Kubectl

Kubernetes Deployments

  • you can deploy your containerized applications on top of a running k8s cluster

    • to do so, you create a Kubernetes Deployment configuration that instructs Kubernetes how to create and update instances of your application

  • once you have a Deployment, the k8s master schedules application instances within the Deployment to run on individual Nodes in the cluster

  • Kubernetes Deployment Controller continuously monitors application instances once the application instances are created

    • if the Node hosting an instance goes down or is deleted, the Deployment controller replaces the instance with an instance on another Node in the cluster

    • this is a self-healing mechanism to address machine failure or maintenance

      • fundamentally different approach to application management than installation scripts that would be used to start applications but did not allow recovery from machine failure

Deploying your first app on Kubernetes

  • Kubectl: the Kubernetes command line interface

    • you can create and manage Deployments using Kubectl

  • Kubectl uses the Kubernetes API to interact with the cluster

Applications need to be packaged into one of the supported container formats in order to be deployed on Kubernetes

  • when you create a Deployment, you'll need to specify:

    • the container image for your application

    • the number of replicas that you want to run

  • you can change this information later by updating your Deployment

  • a Pod is the basic execution unit of a Kubernetes application

  • each Pod is a part of a workload that is running on your cluster

kubectl basics

  • common format of a kubectl command is kubectl {{ action }} {{ resource }}

    • performs the action on the resource

    • you can use --help after the command to get additional info about possible parameters (e.g. kubectl get nodes -- help)

kubectl version - check that kubectl can talk to your cluster

$ kubectl version
Client Version: version.Info{Major:"1", Minor:"17", GitVersion:"v1.17.3", GitCommit:"06ad960bfd03b39c8310aaf92d1e7c12ce618213", GitTreeState:"clean", BuildDate:"2020-02-11T18:14:22Z", GoVersion:"go1.13.6", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"17", GitVersion:"v1.17.3", GitCommit:"06ad960bfd03b39c8310aaf92d1e7c12ce618213", GitTreeState:"clean", BuildDate:"2020-02-11T18:07:13Z", GoVersion:"go1.13.6", Compiler:"gc", Platform:"linux/amd64"}

kubectl get nodes - view the nodes in the cluster

$ kubectl get nodes
minikube   Ready    master   3m43s   v1.17.3
  • Kubernetes will choose where to deploy the app based on Node available resources

Deploy our app

kubectl create deployment - deploy app

  • you need to provide:

    • deployment name

    • app image location (include the full repository url for images hosted outside Docker hub)

$ kubectl create deployment kubernetes-bootcamp
deployment.apps/kubernetes-bootcamp created
  • creating this deployment did the following:

    • searched for a node where an instance of the application could be run

    • scheduled the application to run on that Node

    • configured the cluster to reschedule the instance on a new Node when needed

get deployments - list your deployments

$ kubectl get deployments
NAME                  READY   UP-TO-DATE   AVAILABLE   AGE
kubernetes-bootcamp   1/1     1            1           2m46s
  • there is 1 deployment running a single instance of your app

    • instance is running inside a Docker container on your node

View our app

  • pods within Kubernetes are running on a private, isolated network

    • visible by other pods and services by default if they are within the same kubernetes cluster

    • not visible by other pods and services outside the network

  • kubectl allows us to interact through an API endpoint to communicate with our application

  • the kubectl command creates a proxy that forwards communication into the cluster-wide, private network

  • you can terminate the proxy by using control + C and it won't show any output while it is running

  • open a second terminal window to run the proxy

kubectl proxy- run the proxy

$ kubectl proxy
Starting to serve on
  • proxy acts as a connection between the host (online terminal) and the Kubernetes cluster

    • proxy allows direct access to the API from the terminals

  • you can see all the APIs hosted through the proxy endpoint

curl http://localhost:8001/version - query the version directly through the api using the curl command

$ curl http://localhost:8001/version
  "major": "1",
  "minor": "17",
  "gitVersion": "v1.17.3",
  "gitCommit": "06ad960bfd03b39c8310aaf92d1e7c12ce618213",
  "gitTreeState": "clean",
  "buildDate": "2020-02-11T18:07:13Z",
  "goVersion": "go1.13.6",
  "compiler": "gc",
  "platform": "linux/amd64"
  • if port 8001 is not accessible, ensure that the kubectl proxy is still running

  • the API server will automatically create an endpoint for each pod based on the pod name that is accessible through the proxy

export POD_NAME=$(kubectl get pods -o go-template --template '') echo Name of the Pod: $POD_NAME- get the name of the pod and store it in the POD_NAME environment variable

$ export POD_NAME=$(kubectl get pods -o go-template --template '{{range .items}}{{}}{{"\n"}}{{end}}')
$ echo Name of the Pod: $POD_NAME
Name of the Pod: kubernetes-bootcamp-69fbc6f4cf-rss6f
  • in order for the new deployment to be accessible without using the Proxy, a Service is required

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