Skip to main content

Kubernetes: 1. Pod

CREATE NEW POD

Every kubernetes pod has 4 root level properties. They are

  1. apiVersion
  2. kind
  3. metadata
  4. spec

For a pod these are as below.
metadata -> Data about the Pod, note that we cannot have anything we want here. Only allowed values have to be used.
metadata -> labels. This can be any key:value pairs, think of this as custom properties. 
spec -> containers -> "- name". This is list, because we can have multiple containers running in a pod. "-" Indicates its a list

pod-definition.yaml
apiVersion: v1
kind: Pod
metadata:
  name: myapp-pod
  labels:
    app: myapp
    location: IN

spec:
  containers:
  - name: nginx-container
    image: nginx
  - name: backend-db
    image: redis

The easy way to create a pod is using kubectl run
kubectl run <pod-name> --image=<image-name>


DELETE A POD
Get the list of pods running and then delete the pod
kubectl get pods

kubectl delete pod <pod-name

kubectl delete -f <pod-definition-file> -f 
-> Filename, directory, or URL to a file containing the resource to delete.


UPDATE A POD
There are two ways to update a pod
  1. kubectl edit pod <pod-name> -> You will observe that full definition of pod as created by kubernetes will be shown
    With this the changes are automatically applied to the pod and the pod is restarted
  2. Directly update the YAML file and use kubectl apply command
    With this the changes are updated only after running the kubectl apply command

Note that Kubernetes does not allow many properties of the pod to be changed once created. Below specifications are NOT ALLOWED to be changed.
  • spec.containers[*].image
  • spec.initContainers[*].image
  • spec.activeDeadlineSeconds
  • spec.tolerations

But if you need to make certain changes, then there are 2 options
  1. Use kubectl edit pod
  2. Extract pod output in YAML format and make changes
  • With kubectl edit pod, kubernetes gives an error that the changes cannot be made
  • But at the same time kubernetes makes a copy of the changes under /tmp directory. It gives the full path for the definition file
  • Simply delete the existing pod and recreate the new pod using the updated definition file
  • With second option, get the pod output in yaml format by using "-o yaml" option
  • Update the yaml file with new changes
  • Delete the old pod and create the new pod with the updated yaml file
  • As we can see both the options are bit painful, that is why it is better to create a deployment file
  • Kubernetes allow changes to the deployment definition
  • This is because kubernetes deletes all the pod templates defined in deployment and re-creates the pod everytime there is a change to deployment definition

kubectl edit pod <pod-name>

kubectl apply -f <pod-definition-yaml-file-name>

kubectl get pod webapp -o yaml > my-new-pod.yaml

Labels:

Comments

Post a Comment

Popular posts from this blog

Azure Active Directory

Azure Active directory (AAD) is a Identity as a Service. This is a smaller subset of Active directory. This is not a replacement to active directory at all. Azure active directory provides the identity services to the mobile apps and web apps in Private cloud. These apps may be connected to on-premise applications. So an SSO is enabled for these apps. So Azure active directory has very simple functionality. Create Users, Groups. Map groups to network security groups and provide the authentication to the resources. When you login to Azure portal, right upper corner of the screen has username along with the domain. Domain or tenant or organization are used interchangeably. Management of Users and Groups: Cloud identity (create users manually)  Directory synchronized identifiers (users are synchronized)  Add users Adding a cloud identity users makes the user as Guest When you do directory synchronization on Premise AD Groups are synched up wi...
Post a Comment
Read more

Kubernetes: 19. Configure Application

Configuring application consists of Configuring commands and arguments on applications Configuring environment variables Configuring secrets Docker Commands docker run ubuntu  -> Runs ubuntu container and exit, container CMD is set to [bash], so the container quitely exits docker run ubuntu echo "Hello World" -> Runs ubuntu container, prints "Hello World" exits quitely. To update the default settings, create your own image from the base image lets call this ubuntu-sleeper image FROM ubuntu CMD sleep 5 CMD can also be mentioned in the JSON format like CMD ["sleep", "5"] Note that with JSON format the first element should always be the command to execute,  for eg, it CANNOT be ["sleep 5"] Run build the new ubuntu-sleeper image and run the new image docker build -t ubuntu-sleeper .  -> Build the image docker run ubuntu-sleeper -> Run the new image So the new image will launch ubuntu container, sleep for 5 seconds and quitely ex...
Post a Comment
Read more

Kubernetes: 5. Services

A  service  is a stable endpoint to connect to "something" An abstract way to expose an application running on a set of pods as a network service. Services enable communication between various components within and outside of the application With Kubernetes Services there is no need to configure the application for service discovery Kubernetes Service is an object just like Pod, ReplicaSet etc There is always a service running when Kubernetes is installed, Kubernetes API itself When a service is created, kubernetes creates the endpoints (kubectl get endpoints) The endpoints has all the pods associated with that service Headless Service A headless service is obtained by setting clusterIP  field to None Since there is no virtual IP address, there is no load balancer either The DNS service will return the pods' IP addresses as multiple A records This gives us an easy way to discover all the replicas for a deployment This is useful for creating stateful service...
Post a Comment
Read more