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Summary - Troubleshooting

Combine logs, exec and describe to solve a Pod issue.

Summary: troubleshooting

The troubleshooting order:

  1. kubectl get pods: what do STATUS and RESTARTS say?
  2. kubectl describe pod: the Events section (image, scheduling, mounts, probes).
  3. kubectl logs (--previous, -c, -l): the application's own error message.
  4. kubectl exec / debug: environment, DNS, connectivity from inside.
  5. For service problems: is the EndpointSlice empty, does the selector match?
ImagePullBackOff   -> image name / imagePullSecrets
CrashLoopBackOff   -> logs --previous, exit code
Pending            -> describe: FailedScheduling
CreateContainerConfigError -> missing ConfigMap/Secret

Practice Debug the service

Write three commands: print the web service's selector with jsonpath='{.spec.selector}'; list the pods with their labels; list the EndpointSlices of the web service with -l kubernetes.io/service-name=web.

Starter code

terminal
# buraya yaz

Sample solution

terminal
kubectl get svc web -o jsonpath='{.spec.selector}'
kubectl get pods --show-labels
kubectl get endpointslices -l kubernetes.io/service-name=web

Expected output

{"app":"web-on"}
NAME                  READY   STATUS    LABELS
web-7c5b9f6d8-abcde   1/1     Running   app=web,pod-template-hash=7c5b9f6d8
NAME        ADDRESSTYPE   PORTS     ENDPOINTS
web-x7k2p   IPv4          <unset>   <unset>

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 The pod is Running and READY 1/1, but requests to the service address time out. What should be checked first?

  • The service's EndpointSlice and whether the selector matches the pod labels Correct answer
  • The image version
  • The node count
  • The kubeconfig file

Explanation: If the pod is healthy, the problem is usually the link between service and pod (selector or targetPort).

2 Look at the pod's events first.

Question 
kubectl ____ pod api-xyz
Answer 
kubectl describe pod api-xyz

Explanation: describe pod includes the Events section.

3 Match the symptoms.

Term Meaning
ImagePullBackOff Image problem
CrashLoopBackOff The app crashes
Pending Couldn't be placed
CreateContainerConfigError Missing config object

All lessons in Intermediate

1 What is Kubernetes?

  1. What is Kubernetes?
  2. Why Kubernetes?
  3. Cluster architecture
  4. Control plane
  5. Worker node
  6. Summary - What is Kubernetes

2 Minikube

  1. What is Minikube?
  2. Installing Minikube
  3. minikube start
  4. minikube status
  5. minikube dashboard
  6. Summary - Minikube

3 kubectl basics

  1. What is kubectl?
  2. kubectl get
  3. kubectl describe
  4. kubectl apply
  5. kubectl delete
  6. Summary - kubectl

4 Pod

  1. What is a Pod?
  2. Pod YAML
  3. Creating a Pod
  4. Pod status
  5. Multi-container Pod
  6. Summary - Pod

5 Deployment

  1. What is a Deployment?
  2. Deployment YAML
  3. Replica count
  4. Rolling update
  5. Rollback
  6. Summary - Deployment

6 ReplicaSet

  1. What is a ReplicaSet?
  2. ReplicaSet YAML
  3. ReplicaSet selector
  4. Scaling
  5. Self-healing
  6. Summary - ReplicaSet

7 Service

  1. What is a Service?
  2. ClusterIP
  3. NodePort
  4. LoadBalancer
  5. Service selector
  6. Summary - Service

8 ConfigMap

  1. What is a ConfigMap?
  2. ConfigMap YAML
  3. Environment variable
  4. Mounting as a volume
  5. kubectl create configmap
  6. Summary - ConfigMap

9 Secret

  1. What is a Secret?
  2. Secret types
  3. Secret YAML
  4. Mounting a Secret
  5. kubectl create secret
  6. Summary - Secret

10 Namespace

  1. What is a Namespace?
  2. kubectl get namespaces
  3. Creating a Namespace
  4. The -n flag
  5. Default Namespace
  6. Summary - Namespace

11 Labels and selectors

  1. What is a label?
  2. Adding labels
  3. Label selector
  4. kubectl get -l
  5. Equality and set selectors
  6. Summary - Labels

12 Project: Multi-tier app

  1. Project design
  2. Database Deployment
  3. Web Deployment
  4. ConfigMap and Secret
  5. Putting it together - multi-tier

13 Troubleshooting

  1. kubectl logs
  2. kubectl exec
  3. kubectl describe pod
  4. CrashLoopBackOff
  5. Pending Pod
  6. Summary - Troubleshooting

14 Intermediate final

  1. Challenge - Pod YAML
  2. Challenge - Deployment
  3. Challenge - Service
  4. Challenge - ConfigMap
  5. Challenge - Intermediate project