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Telepresence uses securityContext.runAsUser=0 to bind to privileged ports #617

ark3 opened this Issue Apr 25, 2018 · 0 comments


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ark3 commented Apr 25, 2018

... and that is disallowed in some cluster configurations.


Some clusters don't allow the processes running in containers in pods to run as root (uid=0). OpenShift is configured this way by default. The Telepresence deployment runs its processes as uid=1000 to avoid running afoul of this restriction. This is encoded into the deployment image by including USER 1000 in the Dockerfile.

Sometimes the user's code wants to bind to a privileged port (port number < 1024, e.g., port 80/443 for HTTP/HTTPS). In that case, the code must run as root. When the Telepresence deployment is run in place of this code (swap-deployment) or otherwise needs to bind to a privileged port (the expose option is passed a low port number), it too must run as root.

Telepresence accomplishes this by using the same deployment image (uid=1000) and setting securityContext.runAsUser=0 in the deployment manifest. This causes Kubernetes to override the uid for the processes launched in the container, similar to passing --user=0 to docker run.

However, some clusters disallow the use of securityContext.runAsUser. Telepresence does not handle this case at the moment. The effect is that the Telepresence deployment never successfully gets a running pod, as the cluster security rules forbid the pod from starting.


While waiting around for the Telepresence to start, if you examine its deployment, you'll see something like this:

$ kubectl get deploy teltest -o yaml
apiVersion: extensions/v1beta1
kind: Deployment
  - lastTransitionTime: 2018-04-25T20:36:56Z
    lastUpdateTime: 2018-04-25T20:36:56Z
    message: 'pods is forbidden: pod.Spec.SecurityContext.RunAsUser is forbidden'                                      
    reason: FailedCreate
    status: "True"
    type: ReplicaFailure
  observedGeneration: 1
  unavailableReplicas: 1

Eventually Telepresence crashes, complaining that it could not find its pod.

RuntimeError: Telepresence pod not found for Deployment 'teltest'.

(along with the usual nasty traceback and plea to file an issue)


The straightforward fix to this issue is to avoid using securityContext.runAsUser=0 to run as root. When the user asks for a privileged port, launch a different image that does not include USER=1000 in its Dockerfile.

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