Customizing containerd

Running sandboxed containers using gVisor

For additional security in a Kubernetes cluster it can be useful to run certain containers in a restricted runtime environment known as a sandbox. One option for this is to use gVisor which provides a layer of separation between a running container and the host kernel.

To use gVisor, the necessary executables and containerd configuration can be added to the image generated with image-builder by setting the containerd_gvisor_runtime flag to true. For example, in a packer configuration file:

    "containerd_gvisor_runtime": "true",
    "containerd_gvisor_version": "yyyymmdd",

This will tell image_builder to install runsc, the executable for gVisor, as well as the necessary configuration for containerd. Note that containerd_gvisor_version: yyyymmdd can be used to install a specific point release version. The version defaults to latest.

Once you have built your cluster using the new image, you can then create a RuntimeClass object as follows:

kind: RuntimeClass
  # The name the RuntimeClass will be referenced by.
  # RuntimeClass is a non-namespaced resource.
  name: gvisor
handler: gvisor

Now, to run a pod in the sandboxed environment you just need to specify the name of the RuntimeClass using runtimeClassName in the Pod spec:

apiVersion: v1
kind: Pod
  name: test-sandboxed-pod
  runtimeClassName: gvisor
    - name: sandboxed-container
      image: nginx

Once the pod is up and running, you can verify by using kubectl exec to start a shell on the pod and run dmesg. If the container sandbox is running correctly you should see output similar to the following:

root@sandboxed-container:/# dmesg
[    0.000000] Starting gVisor...
[    0.511752] Digging up root...
[    0.910192] Recruiting cron-ies...
[    1.075793] Rewriting operating system in Javascript...
[    1.351495] Mounting deweydecimalfs...
[    1.648946] Searching for socket adapter...
[    2.115789] Checking naughty and nice process list...
[    2.351749] Granting licence to kill(2)...
[    2.627640] Creating bureaucratic processes...
[    2.954404] Constructing home...
[    3.396065] Segmenting fault lines...
[    3.812981] Setting up VFS...
[    4.164302] Setting up FUSE...
[    4.224418] Ready!

You are running a sandboxed container.