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Migrating telemetry and security agents from dockershim

With Kubernetes 1.20 dockershim was deprecated. From the Dockershim Deprecation FAQ you might already know that most apps do not have a direct dependency on runtime hosting containers. However, there are still a lot of telemetry and security agents that has a dependency on docker to collect containers metadata, logs and metrics. This document aggregates information on how to detect these dependencies and links on how to migrate these agents to use generic tools or alternative runtimes.

Telemetry and security agents

There are a few ways agents may run on Kubernetes cluster. Agents may run on nodes directly or as DaemonSets.

Why do telemetry agents rely on Docker?

Historically, Kubernetes was built on top of Docker. Kubernetes is managing networking and scheduling, Docker was placing and operating containers on a node. So you can get scheduling-related metadata like a pod name from Kubernetes and containers state information from Docker. Over time more runtimes were created to manage containers. Also there are projects and Kubernetes features that generalize container status information extraction across many runtimes.

Some agents are tied specifically to the Docker tool. The agents may run commands like docker ps or docker top to list containers and processes or docker logs to subscribe on docker logs. With the deprecating of Docker as a container runtime, these commands will not work any longer.

Identify DaemonSets that depend on Docker

If a pod wants to make calls to the dockerd running on the node, the pod must either:

  • mount the filesystem containing the Docker daemon's privileged socket, as a volume; or
  • mount the specific path of the Docker daemon's privileged socket directly, also as a volume.

For example: on COS images, Docker exposes its Unix domain socket at /var/run/docker.sock This means that the pod spec will include a hostPath volume mount of /var/run/docker.sock.

Here's a sample shell script to find Pods that have a mount directly mapping the Docker socket. This script outputs the namespace and name of the pod. You can remove the grep /var/run/docker.sock to review other mounts.

kubectl get pods --all-namespaces \
-o=jsonpath='{range .items[*]}{"\n"}{.metadata.namespace}{":\t"}{.metadata.name}{":\t"}{range .spec.volumes[*]}{.hostPath.path}{", "}{end}{end}' \
| sort \
| grep '/var/run/docker.sock'
Note: There are alternative ways for a pod to access Docker on the host. For instance, the parent directory /var/run may be mounted instead of the full path (like in this example). The script above only detects the most common uses.

Detecting Docker dependency from node agents

In case your cluster nodes are customized and install additional security and telemetry agents on the node, make sure to check with the vendor of the agent whether it has dependency on Docker.

Telemetry and security agent vendors

We keep the work in progress version of migration instructions for various telemetry and security agent vendors in Google doc. Please contact the vendor to get up to date instructions for migrating from dockershim.

Last modified January 15, 2021 at 10:16 PM PST: migrating from dockershim (b10decb87)