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Debugging CDI

Introduction

There are various instrumentations available for developers debugging CDI. We will keep expanding this document to make our life easier.

DataVolume annotation to retain the transfer pods after completion

Adding the annotation cdi.kubevirt.io/storage.pod.retainAfterCompletion: "true" will cause CDI transfer pods (importer, uploader, cloner) to be retained after a successful or failed completion. This makes debugging and testing easier, as developers can get the pod state and logs after completion. The pods will be deleted when their dv/pvc is deleted, otherwise the user is responsible for deleting them.

For example:

apiVersion: cdi.kubevirt.io/v1beta1
kind: DataVolume
metadata:
  name: dv-pod-retain
  annotations:
      cdi.kubevirt.io/storage.pod.retainAfterCompletion: "true"
spec:
  source:
      http:
         url: "http://mirrors.nav.ro/fedora/linux/releases/33/Cloud/x86_64/images/Fedora-Cloud-Base-33-1.2.x86_64.qcow2"
  storage:
    resources:
      requests:
        storage: 1Gi

Log verbosity

Different levels of verbosity are used in CDI to control the amount of information that is logged. The verbosity level of logs in CDI can be adjusted using a dedicated field in CDIConfig. This feature enables users to control the amount of detail displayed in logs, ranging from minimal to detailed debugging information.

For example:

apiVersion: cdi.kubevirt.io/v1beta1
kind: CDI
# ...
spec:
  config:
    # Overrides the default verbosity level with 4
    logVerbosity: 4

Changing the verbosity level will automatically restart the CDI components to re-initialize the loggers with the new value.

Profiling with pprof

The CDI controller and operator expose pprof endpoints on their metrics server (port 8443) for live runtime profiling which include heap allocations, goroutine stacks, CPU profiles, etc.

Access requires the cdi-pprof-reader ClusterRole:

kubectl create clusterrolebinding pprof-access \
  --clusterrole=cdi-pprof-reader \
  --user=$(kubectl config current-context)

Then port-forward and profile (e.g., heap profile):

kubectl port-forward -n cdi deploy/cdi-deployment 8443
go tool pprof -http=:8080 https+insecure://localhost:8443/debug/pprof/heap