Question: README shows that gvisor does not support Docker-in-a-container

[jpaodev]

I use GKE myself and would like to ask you (the community) for advice regarding running Docker safely within a Kubernetes container.
The README of this project states in the picture https://github.com/nestybox/sysbox/raw/master/docs/figures/sysbox-comparison.png that Docker is not available as a workload inside of a gvisor container.

According to this tutorial: https://gvisor.dev/docs/tutorials/docker-in-gke-sandbox/ this should work however.
Is the picture outdated or am I misunderstanding the security implications when using Docker inside of a gvisor Kubernetes Pod (rootful Docker inside of the gvisor pod, basically the gvisor pod is run with root user, so Docker and further things can be used)

I would like to double check, as I am looking for a secure option that allows installation of packages via apt inside of a container, using Docker and other similar things inside of that Kubernetes pod

Big thanks in advance for any help here! :)

[Lingikaushikreddy]

You're reading it correctly: the comparison figure predates gVisor's Docker support. docs/figures/sysbox-comparison.png was last changed in January 2022 (git log -- docs/figures/sysbox-comparison.png), and the gVisor tutorial you linked is current. Running Docker inside a GKE Sandbox pod is a supported setup now.

What that tutorial requires, and what it means for security:

• The pod asks for capabilities such as SYS_ADMIN and NET_ADMIN, but they are not host capabilities. gVisor's docs are explicit: "gVisor always runs with zero privileges and zero capabilities, regardless of this setting". The capabilities are what the application inside the sandbox perceives, so dockerd can do what it needs against gVisor's user-space kernel (the Sentry), not against the node's kernel.
• Being root in the pod is root inside the sandbox. A container escape from your nested Docker lands in gVisor, not on the node. That is the property you're after, and it's the same reason apt install inside the pod is fine.
• Version matters. The tutorial lists GKE 1.29.0+ for Docker v27 (1.33.2+ on Autopilot) and newer GKE versions for Docker v28/v29. On Autopilot the cluster must be created with --workload-policies=allow-net-admin.
• Storage is a tmpfs (emptyDir mounted at /var/lib/docker), so images and layers use pod memory and disappear with the pod. Bridge and host network drivers are supported.

The trade-offs versus Sysbox are compatibility, performance and operations rather than "one works, one doesn't". gVisor re-implements syscalls in user space, so some workloads behave differently or run slower (heavy I/O especially), but it's a managed checkbox on GKE (Standard and Autopilot). Sysbox runs containers on the host kernel with user-namespace isolation, so software inside behaves more like a VM, and it does support GKE. Its install guide lists GKE with Ubuntu-Containerd or Ubuntu-Docker node images, so it needs a Standard cluster with an Ubuntu node pool; Autopilot does not let you pick node images.