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Kubernetes

What is Kubernetes Pods? Working with Pods

July 26, 2021 comments off
  • Kubernetes run PODS
  • Atomic Unit of Work Scheduling is POD in kubernetes
  • Pod get instansciated from Kubelet
  • Pod contains one or more container e.g docker
  • Pod get assignment of IP from kube proxy
  • Worker may have one or multiple pods
  • Pods is Scheduled to kubelet by Schedular
  • Pods are EMPHERAL. Same POD can not be run. Similar pods you may get
  • PODS is running state as long as “All Container” is running/succeded.
  • Pods has state from PEDNING -> RUNNING -> succeded/failed -> Terminated
  • Pod name must be unique in Namespace

Birth Events of PODS

Example of POD?

apiVersion: v1
kind: Pod
metadata:
  name: nodehelloworld.example.com
  labels:
    app: helloworld
spec:
  containers:
  - name: devopsschool1
    image: scmgalaxy/nginx-devopsschoolv1
    ports:
    - name: nginx-port
      containerPort: 80

Commads for working with POD?

   54  vi pod.yaml
   55  ls
   56  kubectl get ns
   57  kubectl create ns rajesh
   58  clear
   59  ls
   60  kubectl get ns
   61  clear
   62  kubectl get pods
   63  kubectl get pods -n=rajesh
   64  kubectl get pods -n=dev
   65  clear
   66  ls
   67  kubectl create -f pod.yaml
   68  kubectl get pods
   69  clear
   70  kubectl get pods
   71  kubectl create -f pod.yaml
   72  kubectl create -f pod.yaml -n=rajesh
   73  kubectl get pods -n=rajesh
   74  kubectl get pods
   75  kubectl get pods -n=rajesh,dev
   76  kubectl get pods --all-namespaces
   77  clear
   78  kubectl get pods -o wide
   79  ping 10.44.0.1
   80  clear
   81  ls
   82  clear
   83  kubectl get pods
   84  kubectl edit pod nodehelloworld.example.com
   85  kubectl get pods --show-labels
   86  kubectl -h
   87  kubectl get -h
   88  clear
   89  kubectl get pods -h
   90  clear
   91  ls
   92  vi pod.yaml
   93  kubectl apply -f pod.yaml
   94  kubectl get pods --show-labels
   95  clear
   96  ls
   97  kubectl get pods
   98  kubectl delete pod nodehelloworld.example.com
   99  kubectl delete pod nodehelloworld.example.com -n=rajesh
  100  kubectl get pods --all-namespaces
  101  history

pod.yaml

apiVersion: v1
kind: Pod
metadata:
  name: hello-world-pod
spec:
  containers:
  - name: hello-world
    image: gcr.io/google-samples/hello-app:1.0
    ports:
    - containerPort: 80

deployment.yaml

apiVersion: apps/v1
kind: Deployment
metadata:
  name: hello-world
spec:
  replicas: 1
  selector:
    matchLabels:
      app: hello-world
  template:
    metadata:
      labels:
        app: hello-world
    spec:
      containers:
      - name: hello-world
        image: gcr.io/google-samples/hello-app:1.0
        ports:
        - containerPort: 8080

#Start up kubectl get events --watch and background it.
kubectl get events --watch &

#Create a pod...we can see the scheduling, container pulling and container starting.
kubectl apply -f pod.yaml

#Start a Deployment with 1 replica. We see the deployment created, scaling the replica set and the replica set starting the first pod
kubectl apply -f deployment.yaml

#Scale a Deployment to 2 replicas. We see the scaling the replica set and the replica set starting the second pod
kubectl scale deployment hello-world --replicas=2

#We start off with the replica set scaling to 1, then  Pod deletion, then the Pod killing the container 
kubectl scale deployment hello-world --replicas=1

kubectl get pods

#Let's use exec a command inside our container, we can see the GET and POST api requests through the API server to reach the post.
kubectl -v 6 exec -it PASTE_POD_NAME_HERE -- /bin/sh
ps
exit

#Let's look at the running container/pod from the process level on a Node.
kubectl get pods -o wide
ssh aen@c1-node1
ps -aux | grep hello-app
exit

#Now, let's access our Pod's application directly, without a service and also off the Pod network.
kubectl port-forward PASTE_POD_NAME_HERE 80:8080

#Let's do it again, but this time with a non-priviledged port
kubectl port-forward PASTE_POD_NAME_HERE 8080:8080 &

#We can point curl to localhost, and kubectl port-forward will send the traffic through the API server to the Pod
curl http://localhost:8080

#Kill our port forward session.
fg
ctrl+c

kubectl delete deployment hello-world
kubectl delete pods hello-world-pod

How to use & troubleshoot Kubernetes pods?

Troubleshooting and Debugging Commands:

  • explain Documentation of resources
  • describe Show details of a specific resource or group of resources
  • logs Print the logs for a container in a pod
  • attach Attach to a running container
  • exec Execute a command in a container
  • port-forward Forward one or more local ports to a pod
  • cp Copy files and directories to and from containers.
  • auth Inspect authorization
  • run Run a particular image on the cluster

explain Documentation of resources

—

  $ kubectl explain -h
  106  kubectl explain pod
  107  kubectl explain pod.spec
  108  clear
  109  kubectl explain pod.spec.containers
  110  clear
  111  kubectl explain ns
  112  kubectl explain ns.spec
  113  clear
  114  history

describe Show details of a specific resource or group of resources

Examples:
  122  kubectl get pods
  123  kubectl describe pod nodehelloworld.example.com
  124  clear
  125  kubectl get ns
  126  kubectl describe ns dev
  127  kubectl describe -h


  # Describe a node
  kubectl describe nodes kubernetes-node-emt8.c.myproject.internal

  # Describe a pod
  kubectl describe pods/nginx

  # Describe a pod identified by type and name in "pod.json"
  kubectl describe -f pod.json

  # Describe all pods
  kubectl describe pods

  # Describe pods by label name=myLabel
  kubectl describe po -l name=myLabel

  # Describe all pods managed by the 'frontend' replication controller (rc-created pods
  # get the name of the rc as a prefix in the pod the name).
  kubectl describe pods frontend

logs Print the logs for a container in a pod

  138  curl http://10.44.0.1
  139  kubectl logs nodehelloworld.example.com
  140  kubectl logs nodehelloworld.example.com
  141  kubectl get nodes
  142  clear
  143  kubectl logs nodehelloworld.example.com
  144  kubectl logs -h


Examples:
  # Return snapshot logs from pod nginx with only one container
  kubectl logs nginx

  # Return snapshot logs from pod nginx with multi containers
  kubectl logs nginx --all-containers=true

  # Return snapshot logs from all containers in pods defined by label app=nginx
  kubectl logs -lapp=nginx --all-containers=true

  # Return snapshot of previous terminated ruby container logs from pod web-1
  kubectl logs -p -c ruby web-1

  # Begin streaming the logs of the ruby container in pod web-1
  kubectl logs -f -c ruby web-1

  # Begin streaming the logs from all containers in pods defined by label app=nginx
  kubectl logs -f -lapp=nginx --all-containers=true

  # Display only the most recent 20 lines of output in pod nginx
  kubectl logs --tail=20 nginx

  # Show all logs from pod nginx written in the last hour
  kubectl logs --since=1h nginx

  # Show logs from a kubelet with an expired serving certificate
  kubectl logs --insecure-skip-tls-verify-backend nginx

  # Return snapshot logs from first container of a job named hello
  kubectl logs job/hello

  # Return snapshot logs from container nginx-1 of a deployment named nginx
  kubectl logs deployment/nginx -c nginx-1

attach Attach to a running container

  153  kubectl get pods
  154  kubectl attach nodehelloworld.example.com
  155  clear
  156  kubectl attach -h

  37  curl http://10.44.0.1
  38  watch curl http://10.44.0.1

  # Get output from running pod mypod, use the kubectl.kubernetes.io/default-container annotation
  # for selecting the container to be attached or the first container in the pod will be chosen
  kubectl attach mypod

  # Get output from ruby-container from pod mypod
  kubectl attach mypod -c ruby-container

  # Switch to raw terminal mode, sends stdin to 'bash' in ruby-container from pod mypod
  # and sends stdout/stderr from 'bash' back to the client
  kubectl attach mypod -c ruby-container -i -t

  # Get output from the first pod of a ReplicaSet named nginx
  kubectl attach rs/nginx

exec Execute a command in a container

  160  kubectl get pods
  161  kubectl exec nodehelloworld.example.com ls
  162  clear
  163  kubectl exec nodehelloworld.example.com df -kh
  164  kubectl exec nodehelloworld.example.com 'df -kh'
  165  kubectl exec nodehelloworld.example.com 'df -h'
  166  kubectl exec nodehelloworld.example.com 'df'
  167  kubectl exec nodehelloworld.example.com du -sh
  168  clear
  169  kubectl exec nodehelloworld.example.com du
  170  clearks
  171  ckear
  172  clear
  173  kubectl exec -it nodehelloworld.example.com /bin/bash
  174  kubectl exec -h


  # Get output from running 'date' command from pod mypod, using the first container by default
  kubectl exec mypod -- date

  # Get output from running 'date' command in ruby-container from pod mypod
  kubectl exec mypod -c ruby-container -- date

  # Switch to raw terminal mode, sends stdin to 'bash' in ruby-container from pod mypod
  # and sends stdout/stderr from 'bash' back to the client
  kubectl exec mypod -c ruby-container -i -t -- bash -il

  # List contents of /usr from the first container of pod mypod and sort by modification time.
  # If the command you want to execute in the pod has any flags in common (e.g. -i),
  # you must use two dashes (--) to separate your command's flags/arguments.
  # Also note, do not surround your command and its flags/arguments with quotes
  # unless that is how you would execute it normally (i.e., do ls -t /usr, not "ls -t /usr").
  kubectl exec mypod -i -t -- ls -t /usr

port-forward Forward one or more local ports to a pod

  # Listen on ports 5000 and 6000 locally, forwarding data to/from ports 5000 and 6000 in the pod
  kubectl port-forward pod/mypod 5000 6000

  # Listen on ports 5000 and 6000 locally, forwarding data to/from ports 5000 and 6000 in a pod selected by the
deployment
  kubectl port-forward deployment/mydeployment 5000 6000

  # Listen on port 8888 locally, forwarding to 5000 in the pod
  kubectl port-forward pod/mypod 8888:5000

  # Listen on port 8888 on all addresses, forwarding to 5000 in the pod
  kubectl port-forward --address 0.0.0.0 pod/mypod 8888:5000

  # Listen on port 8888 on localhost and selected IP, forwarding to 5000 in the pod
  kubectl port-forward --address localhost,10.19.21.23 pod/mypod 8888:5000

  192  kubectl get pods -o wide
  193  ping 10.44.0.1
  194  clear
  195  ls
  197  kubectl port-forward -h
  199  kubectl get pods -o wide
  200  kubectl port-forward --address 0.0.0.0 pod/nodehelloworld.example.com 8888:80
  202  ifconfig
  203  clear
  204  kubectl port-forward --address 0.0.0.0 pod/nodehelloworld.example.com 8888:80
  205  kubectl port-forward -h

cp Copy files and directories to and from containers.

  212  kubectl get pods
  213  kubectl exec nodehelloworld.example.com ls /tmp
  214  ls
  215  kubectl cp pod.yaml nodehelloworld.example.com:/tmp
  216  kubectl exec nodehelloworld.example.com ls /tmp
  218  kubectl cp nodehelloworld.example.com:/tmp/pod.yaml ./pod1.yaml
  219  ls
  220  kubectl cp -h

  # !!!Important Note!!!
  # Requires that the 'tar' binary is present in your container
  # image.  If 'tar' is not present, 'kubectl cp' will fail.
  #
  # For advanced use cases, such as symlinks, wildcard expansion or
  # file mode preservation consider using 'kubectl exec'.

  # Copy /tmp/foo local file to /tmp/bar in a remote pod in namespace <some-namespace>
  tar cf - /tmp/foo | kubectl exec -i -n <some-namespace> <some-pod> -- tar xf - -C /tmp/bar

  # Copy /tmp/foo from a remote pod to /tmp/bar locally
  kubectl exec -n <some-namespace> <some-pod> -- tar cf - /tmp/foo | tar xf - -C /tmp/bar

  # Copy /tmp/foo_dir local directory to /tmp/bar_dir in a remote pod in the default namespace
  kubectl cp /tmp/foo_dir <some-pod>:/tmp/bar_dir

  # Copy /tmp/foo local file to /tmp/bar in a remote pod in a specific container
  kubectl cp /tmp/foo <some-pod>:/tmp/bar -c <specific-container>

  # Copy /tmp/foo local file to /tmp/bar in a remote pod in namespace <some-namespace>
  kubectl cp /tmp/foo <some-namespace>/<some-pod>:/tmp/bar

  # Copy /tmp/foo from a remote pod to /tmp/bar locally
  kubectl cp <some-namespace>/<some-pod>:/tmp/foo /tmp/bar

auth Inspect authorization

  224  kubectl auth
  225  kubectl auth can-i create pod
  226  kubectl auth can-i create namespace
  227  kubectl auth can-i delete namespace
  228  kubectl auth can-i -h


  # Check to see if I can create pods in any namespace
  kubectl auth can-i create pods --all-namespaces

  # Check to see if I can list deployments in my current namespace
  kubectl auth can-i list deployments.apps

  # Check to see if I can do everything in my current namespace ("*" means all)
  kubectl auth can-i '*' '*'

  # Check to see if I can get the job named "bar" in namespace "foo"
  kubectl auth can-i list jobs.batch/bar -n foo

  # Check to see if I can read pod logs
  kubectl auth can-i get pods --subresource=log

  # Check to see if I can access the URL /logs/
  kubectl auth can-i get /logs/

  # List all allowed actions in namespace "foo"
  kubectl auth can-i --list --namespace=foo

run Run a particular image on the cluster

POD     |   RUNNING  |  Succedd    | Failed
        Container   Container       Container
        is running  Successfully        Failed
                completed
  # Start a nginx pod.
  kubectl run nginx --image=nginx

  # Start a hazelcast pod and let the container expose port 5701.
  kubectl run hazelcast --image=hazelcast/hazelcast --port=5701

  # Start a hazelcast pod and set environment variables "DNS_DOMAIN=cluster" and "POD_NAMESPACE=default" in the
container.
  kubectl run hazelcast --image=hazelcast/hazelcast --env="DNS_DOMAIN=cluster" --env="POD_NAMESPACE=default"

  # Start a hazelcast pod and set labels "app=hazelcast" and "env=prod" in the container.
  kubectl run hazelcast --image=hazelcast/hazelcast --labels="app=hazelcast,env=prod"

  # Dry run. Print the corresponding API objects without creating them.
  kubectl run nginx --image=nginx --dry-run=client

  # Start a nginx pod, but overload the spec with a partial set of values parsed from JSON.
  kubectl run nginx --image=nginx --overrides='{ "apiVersion": "v1", "spec": { ... } }'

  # Start a busybox pod and keep it in the foreground, don't restart it if it exits.
  kubectl run -i -t busybox --image=busybox --restart=Never

  # Start the nginx pod using the default command, but use custom arguments (arg1 .. argN) for that command.
  kubectl run nginx --image=nginx -- <arg1> <arg2> ... <argN>

  # Start the nginx pod using a different command and custom arguments.
  kubectl run nginx --image=nginx --command -- <cmd> <arg1> ... <argN>
How to use & troubleshoot Kubernetes pods?
Rajesh Kumar
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