Knative Debugging Tips

There are new places to look for information as to why a Knative service doesn’t work. Here is a collection of helpful commands and examples.

1. Display the Knative service:

   kn service list
   

   Newer versions of Knative may already give an error indication here:

   NAME         URL                                                                                                                         LATEST          AGE   CONDITIONS   READY   REASON
   helloworld   http://helloworld....appdomain.cloud   helloworld-v3   81m   1 OK / 3     False   RevisionFailed : Revision "helloworld-v4" failed with message: Unable to fetch image "docker.io/ibmcom/kn-helloworld:2": failed to resolve image to digest: failed to fetch image information: GET https://index.docker.io/v2/ibmcom/kn-helloworld/manifests/2: MANIFEST_UNKNOWN: manifest unknown; map[Tag:2].
   

   The error is far right, but clear: “Unable to fetch image “docker.io/ibmcom/kn-helloworlds:2”. There simply is no image with tag 2.

   I have seen other examples, like this:

   $ kn service list
   NAME          URL                                                   LATEST   AGE    CONDITIONS   READY   REASON
   authors-jee   http://authors-jee-knativetutorial.apps-crc.testing            3m7s   0 OK / 3     False   RevisionMissing : Configuration "authors-jee" does not have any ready Revision.
   

   It is normal and to be expected that the revision is not available for some time immediately after the deployment because the application container needs to start first. A revision is ready when the container successfully started. But in this example the revision isn’t available (ready) after over 3 minutes and that is not normal.

2. Check the pod(s):

   kubectl get pod
   

   What do you do if you get this as result:

   No resources found in default namespace.   
   

   This is bad: no pod means no logs to look at.

3. Check the revision status.

   This is a real example:

   $ kubectl get revision
   NAME             CONFIG NAME   K8S SERVICE NAME   GENERATION   READY   REASON
   helloworld-v1    helloworld                       1            False   ContainerMissing
      
   $ kubectl get revision helloworld-v1 -o yaml
     [...]
     status:
       conditions:
       - lastTransitionTime: "2020-05-28T06:42:14Z"  
          message: The target could not be activated.
          reason: TimedOut
          severity: Info
          status: "False"
          type: Active
      - lastTransitionTime: "2020-05-28T06:40:04Z"
         status: Unknown
         type: ContainerHealthy
      - lastTransitionTime: "2020-05-28T06:40:05Z"
         message: '0/1 nodes are available: 1 Insufficient cpu.'
         reason: Unschedulable
         status: "False"
         type: Ready
      - lastTransitionTime: "2020-05-28T06:40:05Z"
         message: '0/1 nodes are available: 1 Insufficient cpu.'
         reason: Unschedulable
         status: "False"
         type: ResourcesAvailable
   

   Here you can see in one of the status messages that we were under CPU pressure in the cluster. The pod was “unschedulable”.

   There is more information on Debugging issues with your application on the Knative docs site.