My kubernetes pods keep crashing with "CrashLoopBackOff" but I can't find any log

This is what I keep getting:

[root@centos-master ~]# kubectl get pods
NAME               READY     STATUS             RESTARTS   AGE
nfs-server-h6nw8   1/1       Running            0          1h
nfs-web-07rxz      0/1       CrashLoopBackOff   8          16m
nfs-web-fdr9h      0/1       CrashLoopBackOff   8          16m

Below is output from describe pods kubectl describe pods

Events:
  FirstSeen	LastSeen	Count	From				SubobjectPath		Type		Reason		Message
  ---------	--------	-----	----				-------------		--------	------		-------
  16m		16m		1	{default-scheduler }					Normal		Scheduled	Successfully assigned nfs-web-fdr9h to centos-minion-2
  16m		16m		1	{kubelet centos-minion-2}	spec.containers{web}	Normal		Created		Created container with docker id 495fcbb06836
  16m		16m		1	{kubelet centos-minion-2}	spec.containers{web}	Normal		Started		Started container with docker id 495fcbb06836
  16m		16m		1	{kubelet centos-minion-2}	spec.containers{web}	Normal		Started		Started container with docker id d56f34ae4e8f
  16m		16m		1	{kubelet centos-minion-2}	spec.containers{web}	Normal		Created		Created container with docker id d56f34ae4e8f
  16m		16m		2	{kubelet centos-minion-2}				Warning		FailedSync	Error syncing pod, skipping: failed to "StartContainer" for "web" with CrashLoopBackOff: "Back-off 10s restarting failed container=web pod=nfs-web-fdr9h_default(461c937d-d870-11e6-98de-005056040cc2)"

I have two pods: nfs-web-07rxz, nfs-web-fdr9h, but if I do kubectl logs nfs-web-07rxz or with -p option I don't see any log in both pods.

[root@centos-master ~]# kubectl logs nfs-web-07rxz -p
[root@centos-master ~]# kubectl logs nfs-web-07rxz

This is my replicationController yaml file: replicationController yaml file

apiVersion: v1 kind: ReplicationController metadata:   name: nfs-web spec:   replicas: 2   selector:
    role: web-frontend   template:
    metadata:
      labels:
        role: web-frontend
    spec:
      containers:
      - name: web
        image: eso-cmbu-docker.artifactory.eng.vmware.com/demo-container:demo-version3.0
        ports:
          - name: web
            containerPort: 80
        securityContext:
          privileged: true

My Docker image was made from this simple docker file:

FROM ubuntu
RUN apt-get update
RUN apt-get install -y nginx
RUN apt-get install -y nfs-common

I am running my kubernetes cluster on CentOs-1611, kube version:

[root@centos-master ~]# kubectl version
Client Version: version.Info{Major:"1", Minor:"3", GitVersion:"v1.3.0", GitCommit:"86dc49aa137175378ac7fba7751c3d3e7f18e5fc", GitTreeState:"clean", BuildDate:"2016-12-15T16:57:18Z", GoVersion:"go1.6.3", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"3", GitVersion:"v1.3.0", GitCommit:"86dc49aa137175378ac7fba7751c3d3e7f18e5fc", GitTreeState:"clean", BuildDate:"2016-12-15T16:57:18Z", GoVersion:"go1.6.3", Compiler:"gc", Platform:"linux/amd64"}

If I run the docker image by docker run I was able to run the image without any issue, only through kubernetes I got the crash.

Can someone help me out, how can I debug without seeing any log?

As @Sukumar commented, you need to have your Dockerfile have a Command to run or have your ReplicationController specify a command.

The pod is crashing because it starts up then immediately exits, thus Kubernetes restarts and the cycle continues.

#Show details of specific pod
kubectl  describe pod <pod name> -n <namespace-name>

# View logs for specific pod
kubectl  logs <pod name> -n <namespace-name>

If you have an application that takes slower to bootstrap, it could be related to the initial values of the readiness/liveness probes. I solved my problem by increasing the value of initialDelaySeconds to 120s as my SpringBoot application deals with a lot of initialization. The documentation does not mention the default 0 (https://kubernetes.io/docs/api-reference/v1.9/#probe-v1-core)

service:
  livenessProbe:
    httpGet:
      path: /health/local
      scheme: HTTP
      port: 8888
    initialDelaySeconds: 120
    periodSeconds: 5
    timeoutSeconds: 5
    failureThreshold: 10
  readinessProbe:
    httpGet:
      path: /admin/health
      scheme: HTTP
      port: 8642
    initialDelaySeconds: 150
    periodSeconds: 5
    timeoutSeconds: 5
    failureThreshold: 10

A very good explanation about those values is given by https://stackoverflow.com/questions/48572691/what-is-the-default-value-of-initialdelayseconds/48578390#48578390.

> The health or readiness check algorithm works like:

> 1. wait for initialDelaySeconds > 2. perform check and wait timeoutSeconds for a timeout > if the number of continued successes is greater than successThreshold return success > 3. if the number of continued failures is greater than failureThreshold return failure otherwise wait periodSeconds and start a new check

In my case, my application can now bootstrap in a very clear way, so that I know I will not get periodic crashloopbackoff because sometimes it would be on the limit of those rates.

I had the need to keep a pod running for subsequent kubectl exec calls and as the comments above pointed out my pod was getting killed by my k8s cluster because it had completed running all its tasks. I managed to keep my pod running by simply kicking the pod with a command that would not stop automatically as in:

kubectl run YOUR_POD_NAME -n YOUR_NAMESPACE --image SOME_PUBLIC_IMAGE:latest --command tailf /dev/null

My pod kept crashing and I was unable to find the cause. Luckily there is a space where kubernetes saves all the events that occurred before my pod crashed.
(#List Events sorted by timestamp)

To see these events run the command:

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

make sure to add a --namespace mynamespace argument to the command if needed

The events shown in the output of the command showed my why my pod kept crashing.

From https://webkul.com/blog/docker-container-will-automatically-stop-run/">This page, the container dies after running everything correctly but crashes because all the commands ended. Either you make your services run on the foreground, or you create a keep alive script. By doing so, Kubernetes will show that your application is running. We have to note that in the Docker environment, this problem is not encountered. It is only Kubernetes that wants a running app.

Update (an example):

Here's how to avoid CrashLoopBackOff, when launching a Netshoot container:

kubectl run netshoot --image nicolaka/netshoot -- sleep infinity

In your yaml file, add command and args lines:

...
containers:
      - name: api
        image: localhost:5000/image-name 
        command: [ "sleep" ]
        args: [ "infinity" ]
...

Works for me.

I observed the same issue, and added the command and args block in yaml file. I am copying sample of my yaml file for reference

 apiVersion: v1
    kind: Pod
    metadata:
      labels:
        run: ubuntu
      name: ubuntu
      namespace: default
    spec:
      containers:
      - image: gcr.io/ow/hellokubernetes/ubuntu
        imagePullPolicy: Never
        name: ubuntu
        resources:
          requests:
            cpu: 100m
        command: ["/bin/sh"]
        args: ["-c", "while true; do echo hello; sleep 10;done"]
      dnsPolicy: ClusterFirst
      enableServiceLinks: true

As mentioned in above posts, the container exits upon creation.

If you want to test this without using a yaml file, you can pass the sleep command to the kubectl create deployment statement. The double hyphen -- indicates a command, which is equivalent of command: in a Pod or Deployment yaml file.

The below command creates a deployment for debian with sleep 1234, so it so it doesn't exit immediately.

kubectl create deployment deb --image=debian:buster-slim -- "sh" "-c" "while true; do sleep 1234; done"

You then have to create a service etc, but you can kubectl exec -it <pod-name> -- sh (or -- bash) into the pod you just created to test it.

I solved this problem I increased memory resource

  resources:
          limits:
            cpu: 1
            memory: 1Gi
          requests:
            cpu: 100m
        memory: 250Mi 

In my case the problem was what Steve S. mentioned:

> The pod is crashing because it starts up then immediately exits, thus Kubernetes restarts and the cycle continues.

Namely I had a Java application whose main threw an exception (and something overrode the default uncaught exception handler so that nothing was logged). The solution was to put the body of main into try { ... } catch and print out the exception. Thus I could find out what was wrong and fix it.

(Another cause could be something in the app calling System.exit; you could use a custom SecurityManager with an overridden checkExit to prevent (or log the caller of) exit; see https://stackoverflow.com/a/5401319/204205.)

I had same issue and now I finally resolved it. I am not using docker-compose file. I just added this line in my Docker file and it worked.

ENV CI=true

Reference: https://github.com/GoogleContainerTools/skaffold/issues/3882

Try rerunning the pod and running

 kubectl get pods --watch

to watch the status of the pod as it progresses.

In my case, I would only see the end result, 'CrashLoopBackOff,' but the docker container ran fine locally. So I watched the pods using the above command, and I saw the container briefly progress into an OOMKilled state, which meant to me that it required more memory.

In my case this error was specific to the hello-world docker image. I used the nginx image instead of the hello-world image and the error was resolved.

Whilst troubleshooting the same issue I found no logs when using kubeclt logs <pod_id>. Therefore I ssh:ed in to the node instance to try to run the container using plain docker. To my surprise this failed also.

When entering the container with:

docker exec -it faulty:latest /bin/sh

and poking around I found that it wasn't the latest version.

A faulty version of the docker image was already available on the instance.

When I removed the faulty:latest instance with:

docker rmi faulty:latest

everything started to work.

i solved this problem by removing space between quotes and command value inside of array ,this is happened because container exited after started and no executable command present which to be run inside of container.

['sh', '-c', 'echo Hello Kubernetes! && sleep 3600']

I had similar issue but got solved when I corrected my zookeeper.yaml file which had the service name mismatch with file deployment's container names. It got resolved by making them same.

apiVersion: v1
kind: Service
metadata:
  name: zk1
  namespace: nbd-mlbpoc-lab
  labels:
    app: zk-1
spec:
  ports:
  - name: client
    port: 2181
    protocol: TCP
  - name: follower
    port: 2888
    protocol: TCP
  - name: leader
    port: 3888
    protocol: TCP
  selector:
    app: zk-1
---
kind: Deployment
apiVersion: extensions/v1beta1
metadata:
  name: zk-deployment
  namespace: nbd-mlbpoc-lab
spec:
  template:
    metadata:
      labels:
        app: zk-1
    spec:
      containers:
      - name: zk1
        image: digitalwonderland/zookeeper
        ports:
        - containerPort: 2181
        env:
        - name: ZOOKEEPER_ID
          value: "1"
        - name: ZOOKEEPER_SERVER_1
          value: zk1

In my case, the issue was a misconstrued list of command-line arguments. I was doing this in my deployment file:

...
args:
  - "--foo 10"
  - "--bar 100"

Instead of the correct approach:

...
args:
  - "--foo"
  - "10"
  - "--bar"
  - "100"

I finally found the solution when I execute 'docker run xxx ' command ,and I got the error then.It is caused by incomplete-platform .

It seems there could be a lot of reasons why a Pod should be in crashloopbackoff state.

In my case, one of the container was terminating continuously due to the missing Environment value.

So, the best way to debug is to -

1. check Pod description output i.e. kubectl describe pod abcxxx
2. check the events generated related to the Pod i.e. kubectl get events| grep abcxxx
3. Check if End-points have been created for the Pod i.e. kubectl get ep
4. Check if dependent resources have been in-place e.g. CRDs or configmaps or any other resource that may be required.