One of the best practices for your Security posture with GKE is to use a cos-containerd image type for your GKE nodes.

Based on Chromium OS, Container-Optimized OS from Google implements several security design principles to provide a well-configured platform for running production services.

The containerd runtime is considered more resource efficient and secure when compared to the Docker runtime.

Recently, I was curious to know the versions of containerd and COS of my GKE nodes. Let’s see how we could get these information.

Let’s create a new dedicated cluster as the setup for the following command lines throughout this blog article:

zone=us-east4-a
clusterName=test-cos-versions
gcloud container clusters create $clusterName \
    --zone=$zone \
    --image-type cos_containerd \
    --release-channel stable \
    --num-nodes 2

We created a GKE cluster in the stable channel. kubectl get nodes -o wide gives the following information:

VERSION           KERNEL-VERSION   CONTAINER-RUNTIME
v1.19.12-gke.2101 5.4.109+         containerd://1.4.3

We know that we are with the 5.4.109+ of the COS’s KERNEL-VERSION and 1.4.3 of containerd. By using the default version of the channel, we could find the information about which specific version of COS we are using from here: cos-85-13310-1308-1 (dated from Jul 12, 2021 for COS 85).

Now let’s update our cluster to the next version available in the stable channel and see what we’ll have with this new version:

newVersion=1.19.13-gke.701 # latest version for the stable channel when I wrote this blog
gcloud container clusters upgrade $clusterName --master \
    --zone $zone \
    --cluster-version $newVersion \
    --quiet
gcloud container clusters upgrade $clusterName \
    --zone $zone \
    --quiet

kubectl get nodes -o wide now gives the following information:

VERSION           KERNEL-VERSION   CONTAINER-RUNTIME
1.19.13-gke.701   5.4.129+         containerd://1.4.6

Let’s check the exact COS version by running this ephemeral container (or you could ssh to the GCE):

node=$(kubectl get nodes -o jsonpath='{.items[0].metadata.name}')
kubectl debug -it node/$node --image=busybox -- cat /host/etc/os-release

We could see that the version is now cos-85-13310.1308.1 (dated from Jul 12, 2021 for COS 85).

Now let’s update our cluster to the next channel regular and see what we’ll have with this new version:

# Change the release channel:
gcloud container clusters update $clusterName \
    --zone $zone \
    --release-channel regular
# Update the controlplane first with the default version of the new release channel:
gcloud container clusters upgrade $clusterName \
    --zone $zone \
    --master \
    --quiet
# Update nodepools to align the controlplane:
gcloud container clusters upgrade $clusterName \
    --zone $zone \
    --quiet

From there we could repeat the previous command lines in order to get the containerd and the COS versions for the different GKE versions. As the result, the table below will summarize the different versions found for the three channels: stable, regular and rapid:

Channel Kubernetes Kernel COS containerd
stable 1.19.12-gke.2101 5.4.109 cos-85-13310-1308-1 1.4.3
stable 1.19.13-gke.701 5.4.129 cos-85-13310.1308.1 1.4.6
regular 1.20.9-gke.701 5.4.120 cos-89-16108.470.1 1.4.4
regular 1.20.9-gke.1001 5.4.120 cos-89-16108.470.1 1.4.4
rapid 1.21.3-gke.2001 5.4.120 cos-89-16108.470.11 1.4.4
rapid 1.21.4-gke.301 5.4.120 cos-89-16108.470.11 1.4.4

Here are few statements (which will change in the future since updates for GKE or COS happen every week):

  • COS doesn’t have latest containerd version, we see 1.4.3, 1.4.4 or 1.46 as opposed to latest today 1.4.9 or 1.5.5
  • GKE doesn’t have the latest COS version, 85-13310-1308-1, 89-16108.470.1 or 89-16108.470.11 as opposed to latest or lts 89-16108-534-2 (gcloud compute images list --project cos-cloud --no-standard-images)

Is it an issue? Not at all! Because GKE integrates well tested and stable COS images and provide guidance with its security bulletins when necessary.

Is it something to keep in mind? Yes for sure!

Note: on 2021-11-19, GKE got the version v1.22.3-gke.700 with associated containerd version 1.5.4, COS 93 version cos-93-16623-39-6 and COS Kernel version 5.10.68.

When dealing with a manged Kubernetes service, in this case GKE, there is a shared responsibilities model to have in mind. And one of them is to make sure your GKE cluster is up-to-date, node auto-upgrade to the rescue! Node auto-upgrade is upgrading your cluster to the new default version of channel of your GKE cluster. You may also want in some cases to manually update your cluster to the latest version in that channel.

In addition to by default secured features enabled, here is also couple of features you could leverage in order to mitigate let’s say a known CVE on your GKE nodes:

Complementary and further resources:

Hope you enjoyed that one, stay safe out there, cheers!