Troubleshooting

Debug any application

Create test Namespace:

kubectl create ns test

Deploy the backend application:

kubectl create deployment -n test backend --image=k8s.gcr.io/pause:3.1 --replicas=3

See created Deployment

apiVersion: apps/v1
kind: Deployment
metadata:
  creationTimestamp: null
  labels:
    app: backend
  name: backend
  namespace: test
spec:
  replicas: 3
  selector:
    matchLabels:
      app: backend
  strategy: {}
  template:
    metadata:
      creationTimestamp: null
      labels:
        app: backend
    spec:
      containers:
      - image: k8s.gcr.io/pause:3.1
        name: pause
        resources: {}
status: {}

Check the application status:

kubectl get deploy,rs,pods -n test -o wide

Check the Events in the test Namespace:

kubectl get events --sort-by=.metadata.creationTimestamp -n test

Expose test application with Service:

kubectl expose deployment -n test backend --port=80 --target-port=8080

See created Service

apiVersion: v1
kind: Service
metadata:
  creationTimestamp: null
  labels:
    app: backend
  name: backend
  namespace: test
spec:
  ports:
  - port: 80
    protocol: TCP
    targetPort: 8080
  selector:
    app: backend
status:
  loadBalancer: {}

Now we can start verifying if the test application works properly:

kubectl logs -n test -l app=backend

Try open the terminal:

kubectl exec -n test -ti POD_NAME -- bash
kubectl exec -n test -ti POD_NAME -- sh
kubectl exec -n test -ti POD_NAME -- zsh

Try to open the port and make a test connection:

kubectl port-forward -n test pod/POD_NAME 8080:80 &

Test with curl:

curl http://127.0.0.1:8080

Since we've observed that the application isn't working, and we can't connect to it, we need to attach our own debug container:

kubectl debug -n test -ti --image=debian POD_NAME --target=pause -- bash
# apt update
# apt install procps iproute2 dnsutils
# ps faxuw
# ip a
# ip r
# cat /etc/resolv.conf
# nslookup backend 10.96.0.10
# cd /proc/1/root
# ls

Clean up

kubectl delete ns test