Here is a list of 100 kubectl commands that can be useful for diagnosing issues in a Kubernetes cluster.

Cluster Information:

1. Show the Kubernetes version: kubectl version

2. Display cluster information: kubectl cluster-info

3. List all nodes in the cluster: kubectl get nodes

4. Describe a specific node: kubectl describe node <node-name>

5. List all namespaces: kubectl get namespaces

6. List all pods in all namespaces: kubectl get pods --all-namespaces

Pod Diagnostics:

1. List pods in a specific namespace: kubectl get pods -n <namespace>

2. Describe a pod: kubectl describe pod <pod-name> -n <namespace>

3. View pod logs: kubectl logs <pod-name> -n <namespace>

4. Tail pod logs: kubectl logs -f <pod-name> -n <namespace>

5. Execute a command in a pod: kubectl exec -it <pod-name> -n <namespace> -- <command>

Pod Health Checks:

1. Check pod readiness: kubectl get pods <pod-name> -n <namespace> -o jsonpath='{.status.conditions[?(@.type=="Ready")].status}'

2. Check pod events: kubectl get events -n <namespace> --field-selector involvedObject.name=<pod-name>

Service Diagnostics:

1. List all services in a namespace: kubectl get svc -n <namespace>

2. Describe a service: kubectl describe svc <service-name> -n <namespace>

Deployment Diagnostics:

1. List all deployments in a namespace: kubectl get deployments -n <namespace>

2. Describe a deployment: kubectl describe deployment <deployment-name> -n <namespace>

3. View rollout status: kubectl rollout status deployment/<deployment-name> -n <namespace>

4. View rollout history: kubectl rollout history deployment/<deployment-name> -n <namespace>

StatefulSet Diagnostics:

1. List all StatefulSets in a namespace: kubectl get statefulsets -n <namespace>

2. Describe a StatefulSet: kubectl describe statefulset <statefulset-name> -n <namespace>

ConfigMap and Secret Diagnostics:

1. List ConfigMaps in a namespace: kubectl get configmaps -n <namespace>

2. Describe a ConfigMap: kubectl describe configmap <configmap-name> -n <namespace>

3. List Secrets in a namespace: kubectl get secrets -n <namespace>

4. Describe a Secret: kubectl describe secret <secret-name> -n <namespace>

Namespace Diagnostics:

1. Describe a namespace: kubectl describe namespace <namespace-name>

Resource Usage:

1. Check resource usage for a pod: kubectl top pod <pod-name> -n <namespace>

2. Check resource usage for nodes: kubectl top nodes

Networking Diagnostics:

1. Show the IP addresses of pods in a namespace: kubectl get pods -n <namespace -o custom-columns=POD:metadata.name,IP:status.podIP --no-headers

2. List all network policies in a namespace: kubectl get networkpolicies -n <namespace>

3. Describe a network policy: kubectl describe networkpolicy <network-policy-name> -n <namespace>

Persistent Volume (PV) and Persistent Volume Claim (PVC) Diagnostics:

1. List PVs: kubectl get pv

2. Describe a PV: kubectl describe pv <pv-name>

3. List PVCs in a namespace: kubectl get pvc -n <namespace>

4. Describe a PVC: kubectl describe pvc <pvc-name> -n <namespace>

Node Diagnostics:

1. Get the list of pods running on a specific node: kubectl get pods --field-selector spec.nodeName=<node-name> -n <namespace>

Resource Quotas and Limits:

1. List resource quotas in a namespace: kubectl get resourcequotas -n <namespace>

2. Describe a resource quota: kubectl describe resourcequota <resource-quota-name> -n <namespace>

Custom Resource Definitions (CRD) Diagnostics:

1. List custom resources in a namespace: kubectl get <custom-resource-name> -n <namespace>

2. Describe a custom resource: kubectl describe <custom-resource-name> <custom-resource-instance-name> -n <namespace>

Remember to replace <namespace>, <pod-name>, <service-name>, <deployment-name>, <statefulset-name>, <configmap-name>, <secret-name>, <namespace-name>, <pv-name>, <pvc-name>, <node-name>, <network-policy-name>, <resource-quota-name>, <custom-resource-name>, and <custom-resource-instance-name> with your specific values when using these commands. These commands should help you diagnose various aspects of your Kubernetes cluster and applications running within it.

Resource Scaling and Autoscaling:

1. Scale a deployment: kubectl scale deployment <deployment-name> --replicas=<replica-count> -n <namespace>

2. Set autoscaling for a deployment: kubectl autoscale deployment <deployment-name> --min=<min-pods> --max=<max-pods> --cpu-percent=<cpu-percent> -n <namespace>

3. Check horizontal pod autoscaler status: kubectl get hpa -n <namespace>

Job and CronJob Diagnostics:

1. List all jobs in a namespace: kubectl get jobs -n <namespace>

2. Describe a job: kubectl describe job <job-name> -n <namespace>

3. List all cron jobs in a namespace: kubectl get cronjobs -n <namespace>

4. Describe a cron job: kubectl describe cronjob <cronjob-name> -n <namespace>

Volume Diagnostics:

1. List persistent volumes (PVs) sorted by capacity: kubectl get pv --sort-by=.spec.capacity.storage

2. Check PV reclaim policy: kubectl get pv <pv-name> -o=jsonpath='{.spec.persistentVolumeReclaimPolicy}'

3. List all storage classes: kubectl get storageclasses

Ingress and Service Mesh Diagnostics:

1. List all ingresses in a namespace: kubectl get ingress -n <namespace>

2. Describe an ingress: kubectl describe ingress <ingress-name> -n <namespace>

3. List all VirtualServices (Istio) in a namespace: kubectl get virtualservices -n <namespace>

4. Describe a VirtualService (Istio): kubectl describe virtualservice <virtualservice-name> -n <namespace>

Pod Network Troubleshooting:

1. Run a network diagnostic pod (e.g., busybox) for debugging: kubectl run -it --rm --restart=Never --image=busybox net-debug-pod -- /bin/sh

2. Test connectivity from a pod to a specific endpoint: kubectl exec -it <pod-name> -n <namespace> -- curl <endpoint-url>

3. Trace network path from one pod to another: kubectl exec -it <source-pod-name> -n <namespace> -- traceroute <destination-pod-ip>

4. Check DNS resolution from a pod: kubectl exec -it <pod-name> -n <namespace> -- nslookup <domain-name>

Config and Resource Validation:

1. Validate a Kubernetes YAML file without applying it: kubectl apply --dry-run=client -f <yaml-file>

2. Validate a pod’s security context and capabilities: kubectl auth can-i list pods --as=system:serviceaccount:<namespace>:<serviceaccount-name>

RBAC and Security:

1. List roles and role bindings in a namespace: kubectl get roles,rolebindings -n <namespace>

2. Describe a role or role binding: kubectl describe role <role-name> -n <namespace>

Service Account Diagnostics:

1. List service accounts in a namespace: kubectl get serviceaccounts -n <namespace>

2. Describe a service account: kubectl describe serviceaccount <serviceaccount-name> -n <namespace>

Node Drain and Uncordon:

1. Drain a node for maintenance: kubectl drain <node-name> --ignore-daemonsets

2. Uncordon a previously drained node: kubectl uncordon <node-name>

Resource Cleanup:

1. Delete a pod forcefully (not recommended): kubectl delete pod <pod-name> -n <namespace> --grace-period=0 --force

Pod Affinity and Anti-Affinity:

1. List pod affinity rules for a pod: kubectl get pod <pod-name> -n <namespace> -o=jsonpath='{.spec.affinity}'

2. List pod anti-affinity rules for a pod: kubectl get pod <pod-name> -n <namespace> -o=jsonpath='{.spec.affinity.podAntiAffinity}'

Pod Security Policies (PSP):

1. List all pod security policies (if enabled): kubectl get psp

Kubernetes Events:

1. View recent cluster events: kubectl get events --sort-by=.metadata.creationTimestamp

2. Filter events by a specific namespace: kubectl get events -n <namespace>

Node Troubleshooting:

1. Check node conditions: kubectl describe node <node-name> | grep Conditions -A5

2. List node capacity and allocatable resources: kubectl describe node <node-name> | grep -E "Capacity|Allocatable"

Ephemeral Containers (Kubernetes 1.18+):

1. Run an ephemeral debugging container: kubectl debug -it <pod-name> -n <namespace> --image=<debug-image> -- /bin/sh

Resource Metrics (Metrics Server required):

1. Get CPU and Memory usage for pods: kubectl top pod -n <namespace>

Kubelet Diagnostics:

1. View kubelet logs on a node: kubectl logs -n kube-system kubelet-<node-name>

Advanced Debugging with Telepresence:

1. Debug a pod with Telepresence: telepresence --namespace <namespace> --swap-deployment <pod-name>

Kubeconfig and Contexts:

1. List available contexts: kubectl config get-contexts

2. Switch to a different context: kubectl config use-context <context-name>

Pod Security Standards (PodSecurity admission controller):

1. List PodSecurityPolicy (PSP) violations: kubectl get psp -A | grep -vE 'NAME|REVIEWED'

Pod Disruption Budget (PDB) Diagnostics:

1. List all PDBs in a namespace: kubectl get pdb -n <namespace>

2. Describe a PDB: kubectl describe pdb <pdb-name> -n <namespace>

Resource Lock Diagnostics (if using resource locks):

1. List resource locks in a namespace: kubectl get resourcelocks -n <namespace>

Service Endpoints and DNS:

1. List service endpoints for a service: kubectl get endpoints <service-name> -n <namespace>

2. Check DNS configuration in a pod: kubectl exec -it <pod-name> -n <namespace> -- cat /etc/resolv.conf

Custom Metrics (Prometheus, Grafana):

1. Query Prometheus metrics: Use kubectl port-forward to access Prometheus and Grafana services to query custom metrics.

Pod Priority and Preemption:

1. List priority classes: kubectl get priorityclasses

Pod Overhead (Kubernetes 1.18+):

1. List overhead in a pod: kubectl get pod <pod-name> -n <namespace> -o=jsonpath='{.spec.overhead}'

Volume Snapshot Diagnostics (if using volume snapshots):

1. List volume snapshots: kubectl get volumesnapshot -n <namespace>

2. Describe a volume snapshot: kubectl describe volumesnapshot <snapshot-name> -n <namespace>

Resource Deserialization Diagnostics:

1. Deserialize and print a Kubernetes resource: kubectl get <resource-type> <resource-name> -n <namespace> -o=json

Node Taints:

1. List node taints: kubectl describe node <node-name> | grep Taints

Mutating and Validating Webhook Configurations:

1. List mutating webhook configurations: kubectl get mutatingwebhookconfigurations

2. List validating webhook configurations: kubectl get validatingwebhookconfigurations

Pod Network Policies:

1. List pod network policies in a namespace: kubectl get networkpolicies -n <namespace>

Node Conditions (Kubernetes 1.17+):

List node conditions: kubectl get nodes -o custom-columns=NODE:.metadata.name,READY:.status.conditions[?(@.type==”Ready”)].status -l ‘node-role.kubernetes.io/worker=’Audit Logs:

1. Retrieve audit logs (if enabled): Check your Kubernetes audit log configuration for the location of audit logs.

Node Operating System Details:

1. Get the node’s OS information: kubectl get node <node-name> -o jsonpath='{.status.nodeInfo.osImage}'

List All Running Pods in All Namespaces (Short Command):

1. List all running pods in all namespaces in a short format: kubectl get pods --all-namespaces

These commands should cover a wide range of diagnostics scenarios in Kubernetes. Make sure to replace placeholders like <namespace>, <pod-name>, <deployment-name>, etc., with actual values specific to your cluster and use case.