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Basics of Pod
0. What is POD learn via Kubectl Explain
kubectl explain pod
KIND: Pod
VERSION: v1
DESCRIPTION:
Pod is a collection of containers that can run on a host. This resource is
created by clients and scheduled onto hosts.
FIELDS:
apiVersion <string>
APIVersion defines the versioned schema of this representation of an
object. Servers should convert recognized schemas to the latest internal
value, and may reject unrecognized values. More info:
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources
kind <string>
Kind is a string value representing the REST resource this object
represents. Servers may infer this from the endpoint the client submits
requests to. Cannot be updated. In CamelCase. More info:
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds
metadata <Object>
Standard object's metadata. More info:
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#metadata
spec <Object>
Specification of the desired behavior of the pod. More info:
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status
status <Object>
Most recently observed status of the pod. This data may not be up to date.
Populated by the system. Read-only. More info:
https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#spec-and-status
1. Create a Pod from Nginx Image
➜ k8sworkshop git:(main) ✗ kubectl run nginx --image=nginx
pod/nginx created
➜ k8sworkshop git:(main) ✗ kubectl get pods
NAME READY STATUS RESTARTS AGE
nginx 1/1 Running 0 25s
2. Create a Pod and Expose a Port
➜ k8sworkshop git:(main) ✗ kubectl run nginx-port --image=nginx --port=80
pod/nginx-port created
➜ k8sworkshop git:(main) ✗ kubectl describe pod nginx-port
Name: nginx-port
Namespace: default
Priority: 0
Service Account: default
Node: minikube/192.168.49.2
Start Time: Mon, 06 Mar 2023 01:44:56 +0530
Labels: run=nginx-port
Annotations: <none>
Status: Running
IP: 172.17.0.4
IPs:
IP: 172.17.0.4
Containers:
nginx-port:
Container ID: docker://8260b161cc305d1cf4060dff9edbd0b05e86d9c4fc441b5a0a51b9dbe35403d3
Image: nginx
Image ID: docker-pullable://nginx@sha256:aa0afebbb3cfa473099a62c4b32e9b3fb73ed23f2a75a65ce1d4b4f55a5c2ef2
Port: 80/TCP
Host Port: 0/TCP
State: Running
Started: Mon, 06 Mar 2023 01:44:59 +0530
Ready: True
Restart Count: 0
Environment: <none>
Mounts:
/var/run/secrets/kubernetes.io/serviceaccount from kube-api-access-ffpjx (ro)
Conditions:
Type Status
Initialized True
Ready True
ContainersReady True
PodScheduled True
Volumes:
kube-api-access-ffpjx:
Type: Projected (a volume that contains injected data from multiple sources)
TokenExpirationSeconds: 3607
ConfigMapName: kube-root-ca.crt
ConfigMapOptional: <nil>
DownwardAPI: true
QoS Class: BestEffort
Node-Selectors: <none>
Tolerations: node.kubernetes.io/not-ready:NoExecute op=Exists for 300s
node.kubernetes.io/unreachable:NoExecute op=Exists for 300s
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal Scheduled 20s default-scheduler Successfully assigned default/nginx-port to minikube
Normal Pulling 20s kubelet Pulling image "nginx"
Normal Pulled 18s kubelet Successfully pulled image "nginx" in 2.236192917s
Normal Created 18s kubelet Created container nginx-port
Normal Started 18s kubelet Started container nginx-port
➜ k8sworkshop git:(main) ✗
3. Output the Manifest File
kubectl run nginx --image=nginx --port=80 --dry-run=client -o yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: nginx
name: nginx
spec:
containers:
- image: nginx
name: nginx
ports:
- containerPort: 80
resources: {}
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
alternative
kubectl run nginx --image=nginx --port=80 --dry-run=client -o yaml > ngnix.yaml
➜ k8sworkshop git:(main) ✗ ls
LICENSE context data ngnix.yaml package.json styles
README.md course.json lessons node_modules pages workshop
components csv next.config.js package-lock.json public
➜ k8sworkshop git:(main) ✗ cat ngnix.yaml
apiVersion: v1
kind: Pod
metadata:
creationTimestamp: null
labels:
run: nginx
name: nginx
spec:
containers:
- image: nginx
name: nginx
ports:
- containerPort: 80
resources: {}
dnsPolicy: ClusterFirst
restartPolicy: Always
status: {}
➜ k8sworkshop git:(main) ✗
4. Delete PODS
k8sworkshop git:(main) ✗ kubectl delete pod nginx
pod "nginx" deleted
➜ k8sworkshop git:(main) ✗ kubectl delete pod --all
pod "nginx-port" deleted
List the Worker Node
kubectl get nodes
Create a new POD from Nginx Image
kubectl run mywebserver --image=nginx
List the PODS that are currently running.
kubectl get pods
Connect inside the POD
kubectl exec -it mywebserver -- bash
You can come out of the POD with CTRL+D
kubectl exec -it mywebserver -- ls -l /
Delete the POD
kubectl delete pod mywebserver
pod-expose-port.yaml
apiVersion: v1
kind: Pod
metadata:
name: nginx-pod
spec:
containers:
- image: nginx
name: democontainer
ports:
- containerPort: 8080
kubectl apply -f pod-expose-port.yaml
kubectl get pods
kubectl describe pod nginx-pod
➜ k8sworkshop git:(main) ✗ kubectl explain pod.spec.containers.ports
KIND: Pod
VERSION: v1
RESOURCE: ports <[]Object>
DESCRIPTION:
List of ports to expose from the container. Not specifying a port here DOES
NOT prevent that port from being exposed. Any port which is listening on
the default "0.0.0.0" address inside a container will be accessible from
the network. Modifying this array with strategic merge patch may corrupt
the data. For more information See
https://github.com/kubernetes/kubernetes/issues/108255. Cannot be updated.
ContainerPort represents a network port in a single container.
FIELDS:
containerPort <integer> -required-
Number of port to expose on the pod's IP address. This must be a valid port
number, 0 < x < 65536.
hostIP <string>
What host IP to bind the external port to.
hostPort <integer>
Number of port to expose on the host. If specified, this must be a valid
port number, 0 < x < 65536. If HostNetwork is specified, this must match
ContainerPort. Most containers do not need this.
name <string>
If specified, this must be an IANA_SVC_NAME and unique within the pod. Each
named port in a pod must have a unique name. Name for the port that can be
referred to by services.
protocol <string>
Protocol for port. Must be UDP, TCP, or SCTP. Defaults to "TCP".
Possible enum values:
- `"SCTP"` is the SCTP protocol.
- `"TCP"` is the TCP protocol.
- `"UDP"` is the UDP protocol.
➜ k8sworkshop git:(main) ✗
Finding a Pod’s Cluster IP
k8s101 git:(main) ✗ kubectl get pod -o wide
NAME READY STATUS RESTARTS AGE IP NODE NOMINATED NODE READINESS GATES
nginx-pod 1/1 Running 0 95s 172.17.0.7 minikube <none> <none>
nginx-port 1/1 Running 0 108m 172.17.0.3 minikube <none> <none>
Finding a Service’s IP
We can find a Service IP using kubectl as well. In this case we will list all services in all namespaces:
➜ k8s101 git:(main) ✗ kubectl get service --all-namespaces
NAMESPACE NAME TYPE CLUSTER-IP EXTERNAL-IP PORT(S) AGE
default kubernetes ClusterIP 10.96.0.1 <none> 443/TCP 114d
kube-system kube-dns ClusterIP 10.96.0.10 <none> 53/UDP,53/TCP,9153/TCP 114d
kube-system metrics-server ClusterIP 10.106.73.183 <none> 443/TCP 36m
kubernetes-dashboard dashboard-metrics-scraper ClusterIP 10.109.38.100 <none> 8000/TCP 110m
kubernetes-dashboard kubernetes-dashboard ClusterIP 10.108.78.110 <none> 80/TCP 110m
➜ k8s101 git:(main) ✗
➜ k8s101 git:(main) ✗ kubectl get pod nginx-pod --template='{{(index (index .spec.containers 0).ports 0).containerPort}}{{"\n"}}'
8080
Last updated 29 Apr 2024, 11:44 +0530 .