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troubleshooting.md

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Troubleshooting

Sidecar injection problems

Tarian pod agent runs as a sidecar container in the monitored pod, watches and validates processes and files based on the registered constraints. In a rare case the sidecar might be failed to be injected. This describes how to resolve it.

Understanding how a sidecar is injected

Firstly, it is really helpful to understand how the pod-agent sidecar is injected. Kubernetes has admission controllers which intercept requests to the Kubernetes API server prior to the persistence of the object. The mutating admission controllers may validate and modify the objects they admit.

Kubernetes provides a way to extend the admission controller via webhook through MutatingAdmissionWebhook. The webhook is registered using the MutatingWebhookConfiguration API object. In tarian, it's installed as a part of tarian-cluster-agent.

kubectl get MutatingWebhookConfiguration

kubectl get MutatingWebhookConfiguration tarian-cluster-agent -o yaml

If you use the default installation, the contents of the webhook configuration would be as follows:

webhooks:
- admissionReviewVersions:
  - v1
  clientConfig:
    service:
      name: tarian-cluster-agent-controller-manager
      namespace: tarian-system
      path: /inject-pod-agent
      port: 443
  rules:
  - apiGroups:
    - ""
    apiVersions:
    - v1
    operations:
    - CREATE
    resources:
    - pods
    scope: '*'

This means, on every pod created, the webhook controller will send a webhook request to tarian-cluster-agent-controller-manager.tarian-system.svc, which is served by pods from tarian-cluster-agent-controller-manager deployment. These pods will modify the pod's spec to include a sidecar container (pod-agent).

When sidecar silently fails to be injected (no error messages)

Enable log-level=debug to see more verbose logs.

helm upgrade tarian-cluster-agent tarian/tarian-cluster-agent --devel -n tarian-system --set clusterAgent.log.level=debug

After the rollout is completed, you should see more logs in tarian-cluster-agent-controller-manager:

kubectl logs deploy/tarian-cluster-agent-controller-manager -n tarian-system -f

Now when a webhook request comes, a log handling a webhook request should show up there. If there is no such log, that means the webhook is not coming to the pod. See the next sections for what could cause a webhook not coming to the service.

The admission controller cannot connect to the webhook service

The default failurePolicy in tarian-cluster-agent MutatingWebhookConfiguration is Ignore, which means it ignores the failure and the pod will still be created without mutation (sidecar silently fails to be injected). While this is good to prevent issues in production, it also hides the error message that is useful for debugging.

To debug, you can temporarily edit the tarian-cluster-agent MutatingWebhookConfiguration and set the failurePolicy to Fail and limit the scope to a specific namespace so that other namespaces can still work.

kubectl edit MutatingWebhookConfiguration tarian-cluster-agent

change to this:

webhooks:
- failurePolicy: Fail
  namespaceSelector:
    matchExpressions:
    - key: kubernetes.io/metadata.name
      operator: In
      values: ["default"]
  rules:
  - apiGroups:
    - ""
    apiVersions:
    - v1
    operations:
    - CREATE
    resources:
    - pods
    scope: "Namespaced"

Now when a pod is created while the webhook failed, an error will be returned as follows:

Error from server (InternalError): error when creating "dev/config/monitored-pod/register.yaml": Internal error occurred: failed calling webhook "tarian-cluster-agent.k8s.tarian.dev": Post "https://tarian-cluster-agent-controller-manager.tarian-system.svc:443/inject-pod-agent?timeout=10s": dial tcp 10.128.245.250:443: connect: connection refused

When that happens, look for why the connection is refused. Is the pod ready? Is there any network policy? Is there any firewall?

Certificate related errors

Error from server (InternalError): error when creating "dev/config/monitored-pod/register.yaml": Internal error occurred: failed calling webhook "tarian-cluster-agent.k8s.tarian.dev": Post "https://tarian-cluster-agent-controller-manager.tarian-system.svc:443/inject-pod-agent?timeout=10s": x509: certificate signed by unknown authority

Tarian webhook server (deployment name: tarian-cluster-agent-controller-manager) by default manages the certificate needed by the webhook admission controller. It's configured in the tarian-cluster-agent MutatingWebhookConfiguration, in caBundle. In some rare conditions, the caBundle field might not be updated yet so that the CA doesn't match with the one used by the webhook server.

If that's the case, you can try to delete the pod in tarian-cluster-agent-controller-manager deployment. A new pod will then be created again and it will try to update the caBundle.