pods.md

pods

• a pod will have a main container which will represent the application
• containers inside a pod communicate each other via localhost and the ports they expose
• a pod will have a unique ip address that other pods can use for communications
• pod also contains: #k8stodo - init container - sidecar containers - volumes - helper containers
• when a pod dies/or is destroyed other objects in container are also destroyed automatically
• port of the pod running on the node is known as target port - if it isnt specified port of the [[services|targetport]] is used
• command and args options in the definition file allows us to change the command to execute and it's arguments provided by the container/image
  • command and args fields are equivalent to [[entrypoint]] and cmd fields in Dockerfile respectively
• [[environment variables]] can be set using env property.
  • it is an array.
  • [[configmaps]] and [[secrets]] can be set as values.

pod creation

• when a request comes in for a new pod, [[kube api server]] creates a new entry for a pod in [[etcd]]
• [[scheduler]] monitoring the situation, assigns the pod to a [[node]] and updates the [[kube api server]] which updates the [[etcd]]
• [[kube api server]] then sends a request to [[kubelet]] on the appropriate [[node]]
• [[kubelet]] then creates the pod and instructs the application runtime engine([[docker]] or [[containerd]]) to deploy the pod
• after the pod is deployed [[kubelet]] updates the status to [[kube api server]] which in turn updates [[etcd]]

init container

sidecar containers

volumes

helper containers

[[pod networking]]

commands

definition

apiVersion: v1
kind: Pod
metadata:
	name: "hello"
    namespace: dev
    label:
        type: backend
        app: myapp
spec:
    containers:
        - name: nginx-server
	      image: nginx:latest
	      command: ["nginx"]
		  args: [""]
		  env:
			  - name: COLOR1
				value: red
			  - name: COLOR2
				valueFrom:
					configMapRef:
						name: app-config
						key: COLOR2
			  - name: COLOR3
				valueFrom:
					secretKeyRef:
		  envFrom:
			  - configMapRef:
					name: app-config
			  - secretRef:
					name: root-pw