Kubernetes-questions

Create a yaml file for pod in cluster

Kubernetes objects

Workload objects define the applications and jobs running in the cluster.

Pod: The smallest deployable unit in Kubernetes. A pod runs one or more containers.
ReplicaSet: Ensures a specified number of pod replicas are running at any given time.
Deployment: Manages ReplicaSets and provides declarative updates for pods and ReplicaSets.
StatefulSet: Manages stateful applications with persistent storage and unique pod identities.
DaemonSet: Ensures that a copy of a pod runs on all or specific nodes in the cluster.
Job: Creates pods to perform a specific task and ensures they complete successfully.
CronJob: Manages jobs that run on a schedule, similar to a cron task.

Few Kubernetes commands:
Sceanrio based question Namespace call tata, there are many service under namespace. Some services failed no pro active alerts Get list of pods that are not in running state, and in-incomplete pods

kubectl get pods -n tata --field-selector=status.phase!=Running

Faulty node one our cluster service hosting in the cluster not responding auto to not fault, I have ip of the node, we wan’t to find the services running in node
```
kubectl get pods -o wide --all-namespaces | grep <node-ip>

##Find Services Linked to Those Pods##

kubectl get svc --all-namespaces | grep <pod-name>
```

List pods with nodes running

kubectl get pods -o wide
    Alternaive
kubectl get pods -o custom-columns="NAME:.metadata.name,NODE:.spec.nodeName"

1) Command to list pods running in which node and which availability zone:

 kubectl get pods -o custom-columns="POD:metadata.name,NODE:spec.nodeName" | tail -n +2 | while read pod node; do
 echo -n "$pod $node "
 kubectl get node "$node" -o jsonpath="{.metadata.labels.topology\.kubernetes\.io/zone}"
 echo ""
 done

2) List of nodes and how many pods running on them:

kubectl get po -o json --all-namespaces | \
 jq '.items | group_by(.spec.nodeName) | map({"nodeName": .[0].spec.nodeName, "count": length}) | sort_by(.count)'

3) List pods using most of RAM and CPU: For CPU:

kubectl top pods -A | sort --reverse --key 3 --numeric

For RAM:

kubectl top pods -A | sort --reverse --key 4 --numeric

4) Getting pods that are continuously restarting (sorting them):

kubectl get pods --all-namespaces -o json | jq -r '.items | sort_by(.status.containerStatuses[0].restartCount) | reverse[] | [.metadata.namespace, .metadata.name, .status.containerStatuses[0].restartCount] | @tsv' | column -t

5) Quickly check the pod limits:

kubectl get pods -o=custom-columns='NAME:spec.containers[*].name,MEMREQ:spec.containers[*].resources.requests.memory,MEMLIM:spec.containers[*].resources.limits.memory,CPUREQ:spec.containers[*].resources.requests.cpu,CPULIM:spec.containers[*].resources.limits.cpu'

6) Get all private IPs of nodes:

kubectl get nodes -o json | \
 jq -r '.items[].status.addresses[]? | select (.type == "InternalIP") | .address' | \
 paste -sd "\n" -

7) Checking logs: Read logs with human readable timestamp:

kubectl logs -f my-pod --timestamps

8. Logs of the pods, last 100 lines —tail

kubectl logs -f my-pod --tail=100

9) Check for events across all namespaces and filter for any errors,

kubectl get events --all-namespaces --field-selector type=Warning -o wide
or 
kubectl get events --all-namespaces --field-selector type!=Normal -o wide

Kubernetes Commands

1. Cluster Information

View Cluster Information:
```
kubectl cluster-info
```
List All Nodes:
```
kubectl get nodes
```
Describe a Node:
```
kubectl describe node <node-name>
```

2. Pod Management

List All Pods:
```
kubectl get pods
```
List Pods in a Specific Namespace:
```
kubectl get pods -n <namespace>
```
View Pod Logs:
```
kubectl logs <pod-name>
```

View Logs for a Specific Container in a Pod:

kubectl logs <pod-name> -c <container-name>

Describe a Pod:
```
kubectl describe pod <pod-name>
```

Execute a Command in a Pod:

kubectl exec -it <pod-name> -- <command>

Delete a Pod:
```
kubectl delete pod <pod-name>
```

3. Deployment Management

List Deployments:
```
kubectl get deployments
```

Describe a Deployment:

kubectl describe deployment <deployment-name>

Scale a Deployment:

kubectl scale deployment <deployment-name> --replicas=<number>

Apply Changes from a YAML File:
```
kubectl apply -f <file.yaml>
```

Roll Back a Deployment:

kubectl rollout undo deployment <deployment-name>

View Deployment History:

kubectl rollout history deployment <deployment-name>

4. Service and Networking

List Services:
```
kubectl get svc
```
Describe a Service:
```
kubectl describe svc <service-name>
```

Port Forward a Service:

kubectl port-forward svc/<service-name> <local-port>:<service-port>

5. Namespace Management

List Namespaces:
```
kubectl get namespaces
```

Create a Namespace:

kubectl create namespace <namespace-name>

Delete a Namespace:

kubectl delete namespace <namespace-name>

6. Troubleshooting

List All Events:
```
kubectl get events
```
Check the Status of All Resources:
```
kubectl get all
```
Debug a Node:
```
kubectl describe node <node-name>
```
Debug a Pod:
```
kubectl describe pod <pod-name>
```

7. Resource Management

Get Resource Usage (using Metrics Server):
```
kubectl top nodes
kubectl top pods
```

Delete a Resource:

kubectl delete <resource-type> <resource-name>

Edit a Resource:

kubectl edit <resource-type> <resource-name>

8. Custom Resources and YAML Files

Validate a YAML File:

kubectl apply --dry-run=client -f <file.yaml>

Delete All Resources Defined in a File:
```
kubectl delete -f <file.yaml>
```
List Custom Resources (CRDs):
```
kubectl get crd
```

9. Utility Commands

Switch Context:

kubectl config use-context <context-name>

View Current Context:
```
kubectl config current-context
```
List All Contexts:
```
kubectl config get-contexts
```

kubernetes Objects

(Kubernetes object)