Application Scheduling and Lifecycle Mangement

This article describs how to use kubernetes deployments to deploy pods, scale pods, perform rolling updates and rollbacks, carry out resource management, and use ConfigMaps to configurepods using kubectl command and YAML definitions.

Run a container

Cretae a pod using am imperative command

Create pods with `kubectl` command

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kubectl run <pod-name> --image=<image-name:image-tag>

for instance:

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kubectl run nginx-pod --image=nginx:alpine

Check the pod’s status

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kubectl describe pod nginx-pod

Create pods with declarative management

Create a yaml file

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apiVersion: v1
kind: Pod
metadata:
  name: nginx
spec:
  containers:
  - name: nginx
  image: nginx:alpine
  ports:
  - containerPort: 80

To create pods with kubectl apply -f file

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kubectl apply -f <your-spec>.yaml

run busybox

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kubctl run busybox --rm -it --image=busybox /bin/sh

export yaml file with –dry-run

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kubectl run nginx --image=nginx:alpine --dry-run -o yaml > nginx-sample.yaml
kubectl apply nginx-sample.yaml

Understanding Liveness, readiness, and startup probes

Liveness probes
Readiness probes
Startup probes

Understanding a multi-conainter pod

Multi-container pods are simply pods with more than one container working together as a single unit. When it coms to multiple containers residing in a pod, a conainer ineracts with another in the following two ways:

Shared networking: When two containers are running on the same host when they are in the same pod, they can access each other by simpley using localhost. All the listening ports are accessible to other containers in the pod, even if they’re not exposed outside the pod.
Shared storage volumes: We can mount the same volume to two different conainers so that they can both interact with the same data - it is possible to have one container write data to the volume and the other container read that data from the same volume. Some volumes even allow concurrent reading and writing.

Create multiple containers in a pod:

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apiVersion: v1
kind: Pod
metadata:
  neme: multi-app-pod
  labels:
    app: multi-app
spec:
  containers:
  - name: nginx
    image: nginx
    ports:
    - containerPort: 80"wq
    - 
  - name: busybox-sidecar
    image: busybox
    command: [ 'sh', '-c', 'while true; do sleep 3600; done;' ]
    

Understanding an init container

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apiVersion: v1
kind: Pod
metadata:
  name: melon-pod
  labels:
    name: melonapp
spec:
  containers:
  - name: melonapp-container
    image: busybox:latest
    command: ['sh', '-c', 'echo The melonapp is running! && sleep 3600']
  initContainers:
  - name: init-melonservice
    image: busybox:latest
    command: ['sh', '-c', 'until nslookup melonservice; do echo waiting for melonserivce; sleep 2; done;']
  - name: init-melondb
    image: busybox:latest
    command: ['sh', '-c', 'until nslookup melondb; do echo waiting for melondb; sleep 2; done;']
    