Kubernetes equivalent of `docker run --init`

Question

It is a recommended best practice to not run dockerized Node.JS applications as PID 1 (see https://github.com/nodejs/docker-node/blob/master/docs/BestPractices.md#handling-kernel-signals) in order to correctly capture signals.

The docker run command provides the --init flag to wrap the application entry point with a small init system that forwards signals correctly.

Is there a built-in equivalent of the --init flag in Kubernetes?

I've explored the Pod and Container object specifications for Kubernetes 1.10 but have not seen anything related to specifying how the image gets started.

An alternative would be to explicitly include and use Tini in every container, but I would really like some way that does it transparently the way the --init flag behaves.

Are there other alternatives?

Answer 1

If you enable process (PID) namespace sharing for your pods, the init process (pause) will come from Kubernetes. If you have a separate process namespace for your containers, they need to include tini or another init process themselves.

According to https://www.ianlewis.org/en/almighty-pause-container, Kubernetes 1.7 had a shared process namespace by default and a kubelet flag to disable it, 1.8 had it off by default and a kubelet flag to enable it. Kubernetes 1.11 has an alpha feature to enable a shared process namespace: https://kubernetes.io/docs/tasks/configure-pod-container/share-process-namespace/

Answer 2

If you suppose that Kubernetes creates a container using Docker commands, then you should be aware that it knows nothing about --init key. In other words, Kubernetes has no such wrapper for starting a container with another initial process.

So, if you want to use this feature in Kubernetes, you need to prepare a Docker image with Tini in it.

Actually, Tini is included in Docker 1.13 or greater, and you just enable it by passing the --init flag to docker run. So, to add Tini to your image, use the following code in the Dockerfile:

# Add Tini
ENV TINI_VERSION <check-version-on-github>
ADD https://github.com/krallin/tini/releases/download/${TINI_VERSION}/tini /tini
RUN chmod +x /tini
ENTRYPOINT ["/tini", "--"]

# Run your program under Tini
CMD ["/your/program", "-and", "-its", "arguments"]